SERVER-23891 implement ShardId class

81 files changed, 719 insertions, 363 deletions

diff --git a/src/mongo/client/parallel.cpp b/src/mongo/client/parallel.cpp
index 4a1f9d010a1..2baf10a58d1 100644
--- a/src/mongo/client/parallel.cpp
+++ b/src/mongo/client/parallel.cpp
@@ -678,7 +678,7 @@ void ParallelSortClusteredCursor::startInit(OperationContext* txn) {
         } catch (SocketException& e) {
             warning() << "socket exception when initializing on " << shardId
                       << ", current connection state is " << mdata.toBSON() << causedBy(e);
-            e._shard = shardId;
+            e._shard = shardId.toString();
             mdata.errored = true;
             if (returnPartial) {
                 mdata.cleanup(true);
@@ -688,7 +688,7 @@ void ParallelSortClusteredCursor::startInit(OperationContext* txn) {
         } catch (DBException& e) {
             warning() << "db exception when initializing on " << shardId
                       << ", current connection state is " << mdata.toBSON() << causedBy(e);
-            e._shard = shardId;
+            e._shard = shardId.toString();
             mdata.errored = true;
             if (returnPartial && e.getCode() == 15925 /* From above! */) {
                 mdata.cleanup(true);
diff --git a/src/mongo/db/SConscript b/src/mongo/db/SConscript
index accf4d71a5d..d02dace87d7 100644
--- a/src/mongo/db/SConscript
+++ b/src/mongo/db/SConscript
@@ -700,6 +700,7 @@ serveronlyLibdeps = [
     "$BUILD_DIR/mongo/s/catalog/replset/sharding_catalog_manager_impl",
     "$BUILD_DIR/mongo/s/client/sharding_connection_hook",
     "$BUILD_DIR/mongo/s/coreshard",
+    "$BUILD_DIR/mongo/s/shard_id",
     "$BUILD_DIR/mongo/s/serveronly",
     "$BUILD_DIR/mongo/scripting/scripting_server",
     "$BUILD_DIR/mongo/util/clock_sources",
diff --git a/src/mongo/db/repl/SConscript b/src/mongo/db/repl/SConscript
index 89d0aac35cc..66b38a9e163 100644
--- a/src/mongo/db/repl/SConscript
+++ b/src/mongo/db/repl/SConscript
@@ -138,6 +138,7 @@ env.Library(
         'oplog_buffer_blocking_queue.cpp',
     ],
     LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
     ],
 )
 
diff --git a/src/mongo/db/s/active_migrations_registry_test.cpp b/src/mongo/db/s/active_migrations_registry_test.cpp
index 6ced2bb68da..dfde342ed39 100644
--- a/src/mongo/db/s/active_migrations_registry_test.cpp
+++ b/src/mongo/db/s/active_migrations_registry_test.cpp
@@ -71,8 +71,8 @@ MoveChunkRequest createMoveChunkRequest(const NamespaceString& nss) {
         nss,
         ChunkVersion(2, 3, OID::gen()),
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
-        "shard0001",
-        "shard0002",
+        ShardId("shard0001"),
+        ShardId("shard0002"),
         ChunkRange(BSON("Key" << -100), BSON("Key" << 100)),
         1024,
         MigrationSecondaryThrottleOptions::create(MigrationSecondaryThrottleOptions::kOff),
diff --git a/src/mongo/db/s/collection_metadata_test.cpp b/src/mongo/db/s/collection_metadata_test.cpp
index 103150d031a..013c135cc84 100644
--- a/src/mongo/db/s/collection_metadata_test.cpp
+++ b/src/mongo/db/s/collection_metadata_test.cpp
@@ -67,7 +67,7 @@ protected:
         // can't load metadata
         ChunkType chunkType;
         chunkType.setNS(NamespaceString{"test.foo"}.ns());
-        chunkType.setShard("shard0001");
+        chunkType.setShard(ShardId("shard0001"));
         chunkType.setMin(BSON("a" << MINKEY));
         chunkType.setMax(BSON("a" << MAXKEY));
         chunkType.setVersion(ChunkVersion(1, 0, epoch));
diff --git a/src/mongo/db/s/merge_chunks_command.cpp b/src/mongo/db/s/merge_chunks_command.cpp
index 4f37d969bf9..2b3ca75a890 100644
--- a/src/mongo/db/s/merge_chunks_command.cpp
+++ b/src/mongo/db/s/merge_chunks_command.cpp
@@ -55,7 +55,7 @@ using std::vector;
 namespace {
 
 BSONArray buildOpPrecond(const string& ns,
-                         const string& shardName,
+                         const ShardId& shardName,
                          const ChunkVersion& shardVersion) {
     BSONArrayBuilder preCond;
     BSONObjBuilder condB;
diff --git a/src/mongo/db/s/metadata_loader.cpp b/src/mongo/db/s/metadata_loader.cpp
index f57fc35a2df..8bc72af7f60 100644
--- a/src/mongo/db/s/metadata_loader.cpp
+++ b/src/mongo/db/s/metadata_loader.cpp
@@ -60,7 +60,7 @@ namespace {
  */
 class SCMConfigDiffTracker : public ConfigDiffTracker<BSONObj> {
 public:
-    SCMConfigDiffTracker(const string& currShard) : _currShard(currShard) {}
+    SCMConfigDiffTracker(const ShardId& currShard) : _currShard(currShard) {}
 
     virtual bool isTracked(const ChunkType& chunk) const {
         return chunk.getShard() == _currShard;
@@ -70,7 +70,7 @@ public:
         return make_pair(chunk.getMin(), chunk.getMax());
     }
 
-    virtual string shardFor(OperationContext* txn, const string& name) const {
+    virtual ShardId shardFor(OperationContext* txn, const ShardId& name) const {
         return name;
     }
 
@@ -79,7 +79,7 @@ public:
     }
 
 private:
-    const string _currShard;
+    const ShardId _currShard;
 };
 
 }  // namespace
@@ -137,7 +137,7 @@ Status MetadataLoader::initChunks(OperationContext* txn,
                                   const string& shard,
                                   const CollectionMetadata* oldMetadata,
                                   CollectionMetadata* metadata) const {
-    map<string, ChunkVersion> versionMap;
+    map<ShardId, ChunkVersion> versionMap;  // TODO: use .h defined type
 
     // Preserve the epoch
     versionMap[shard] = metadata->_shardVersion;
diff --git a/src/mongo/db/s/metadata_loader_test.cpp b/src/mongo/db/s/metadata_loader_test.cpp
index 0825fd2ea6b..c96b77a1590 100644
--- a/src/mongo/db/s/metadata_loader_test.cpp
+++ b/src/mongo/db/s/metadata_loader_test.cpp
@@ -88,7 +88,7 @@ protected:
         // Infer namespace, shard, epoch, keypattern from first chunk
         const ChunkType* firstChunk = *(chunks.vector().begin());
         const string ns = firstChunk->getNS();
-        const string shardName = firstChunk->getShard();
+        const string shardName = firstChunk->getShard().toString();
         const OID epoch = firstChunk->getVersion().epoch();
 
         CollectionType coll;
@@ -276,7 +276,7 @@ TEST_F(MetadataLoaderFixture, CheckNumChunk) {
     // can't load metadata
     ChunkType chunkType;
     chunkType.setNS("test.foo");
-    chunkType.setShard("shard0001");
+    chunkType.setShard(ShardId("shard0001"));
     chunkType.setMin(BSON("a" << MINKEY));
     chunkType.setMax(BSON("a" << MAXKEY));
     chunkType.setVersion(ChunkVersion(1, 0, epoch));
@@ -424,7 +424,7 @@ TEST_F(MetadataLoaderFixture, NoChunks) {
 TEST_F(MetadataLoaderFixture, PromotePendingNA) {
     unique_ptr<ChunkType> chunk(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << MINKEY));
     chunk->setMax(BSON("x" << 0));
     chunk->setVersion(ChunkVersion(1, 0, OID::gen()));
@@ -459,7 +459,7 @@ TEST_F(MetadataLoaderFixture, PromotePendingNAVersion) {
 
     unique_ptr<ChunkType> chunk(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << MINKEY));
     chunk->setMax(BSON("x" << 0));
     chunk->setVersion(ChunkVersion(1, 1, epoch));
@@ -500,7 +500,7 @@ TEST_F(MetadataLoaderFixture, PromotePendingGoodOverlap) {
 
     unique_ptr<ChunkType> chunk(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << MINKEY));
     chunk->setMax(BSON("x" << 0));
     chunk->setVersion(ChunkVersion(1, 0, epoch));
@@ -508,14 +508,14 @@ TEST_F(MetadataLoaderFixture, PromotePendingGoodOverlap) {
 
     chunk.reset(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << 10));
     chunk->setMax(BSON("x" << 20));
     chunks.mutableVector().push_back(chunk.release());
 
     chunk.reset(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << 30));
     chunk->setMax(BSON("x" << MAXKEY));
     chunks.mutableVector().push_back(chunk.release());
@@ -531,7 +531,7 @@ TEST_F(MetadataLoaderFixture, PromotePendingGoodOverlap) {
 
     chunk.reset(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << 0));
     chunk->setMax(BSON("x" << 10));
     chunk->setVersion(ChunkVersion(1, 0, epoch));
@@ -580,7 +580,7 @@ TEST_F(MetadataLoaderFixture, PromotePendingBadOverlap) {
 
     unique_ptr<ChunkType> chunk(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << MINKEY));
     chunk->setMax(BSON("x" << 0));
     chunk->setVersion(ChunkVersion(1, 0, epoch));
@@ -598,7 +598,7 @@ TEST_F(MetadataLoaderFixture, PromotePendingBadOverlap) {
 
     chunk.reset(new ChunkType());
     chunk->setNS("foo.bar");
-    chunk->setShard("shard0000");
+    chunk->setShard(ShardId("shard0000"));
     chunk->setMin(BSON("x" << 15));
     chunk->setMax(BSON("x" << MAXKEY));
     chunk->setVersion(ChunkVersion(1, 0, epoch));
diff --git a/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp b/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
index e5b15ac679d..55b38ec4b47 100644
--- a/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
+++ b/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
@@ -170,7 +170,8 @@ MigrationChunkClonerSourceLegacy::MigrationChunkClonerSourceLegacy(MoveChunkRequ
                                                                    const BSONObj& shardKeyPattern)
     : _args(std::move(request)),
       _shardKeyPattern(shardKeyPattern),
-      _sessionId(MigrationSessionId::generate(_args.getFromShardId(), _args.getToShardId())) {}
+      _sessionId(MigrationSessionId::generate(_args.getFromShardId().toString(),
+                                              _args.getToShardId().toString())) {}
 
 MigrationChunkClonerSourceLegacy::~MigrationChunkClonerSourceLegacy() {
     invariant(!_deleteNotifyExec);
diff --git a/src/mongo/db/s/migration_destination_manager.cpp b/src/mongo/db/s/migration_destination_manager.cpp
index e6990087018..89aab68dcd4 100644
--- a/src/mongo/db/s/migration_destination_manager.cpp
+++ b/src/mongo/db/s/migration_destination_manager.cpp
@@ -421,7 +421,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* txn,
           << " for collection " << ns << " from " << fromShard << " at epoch " << epoch.toString();
 
     string errmsg;
-    MoveTimingHelper timing(txn, "to", ns, min, max, 6 /* steps */, &errmsg, "", "");
+    MoveTimingHelper timing(txn, "to", ns, min, max, 6 /* steps */, &errmsg, ShardId(), ShardId());
 
     ScopedDbConnection conn(fromShard);
 
diff --git a/src/mongo/db/s/migration_source_manager.cpp b/src/mongo/db/s/migration_source_manager.cpp
index 96d32fac9b9..74da4ec2558 100644
--- a/src/mongo/db/s/migration_source_manager.cpp
+++ b/src/mongo/db/s/migration_source_manager.cpp
@@ -317,7 +317,7 @@ Status MigrationSourceManager::commitDonateChunk(OperationContext* txn) {
         n.append(ChunkType::ns(), _args.getNss().ns());
         n.append(ChunkType::min(), _args.getMinKey());
         n.append(ChunkType::max(), _args.getMaxKey());
-        n.append(ChunkType::shard(), _args.getToShardId());
+        n.append(ChunkType::shard(), _args.getToShardId().toString());
         n.done();
 
         BSONObjBuilder q(op.subobjStart("o2"));
@@ -357,7 +357,7 @@ Status MigrationSourceManager::commitDonateChunk(OperationContext* txn) {
         n.append(ChunkType::ns(), _args.getNss().ns());
         n.append(ChunkType::min(), bumpMin);
         n.append(ChunkType::max(), bumpMax);
-        n.append(ChunkType::shard(), _args.getFromShardId());
+        n.append(ChunkType::shard(), _args.getFromShardId().toString());
         n.done();
 
         BSONObjBuilder q(op.subobjStart("o2"));
diff --git a/src/mongo/db/s/move_chunk_command.cpp b/src/mongo/db/s/move_chunk_command.cpp
index 189f7934405..e7f332fe9f3 100644
--- a/src/mongo/db/s/move_chunk_command.cpp
+++ b/src/mongo/db/s/move_chunk_command.cpp
@@ -149,7 +149,7 @@ public:
                 txn, moveChunkRequest.getConfigServerCS().toString());
         }
 
-        shardingState->setShardName(moveChunkRequest.getFromShardId());
+        shardingState->setShardName(moveChunkRequest.getFromShardId().toString());
 
         // Make sure we're as up-to-date as possible with shard information. This catches the case
         // where we might have changed a shard's host by removing/adding a shard with the same name.
diff --git a/src/mongo/db/s/move_timing_helper.cpp b/src/mongo/db/s/move_timing_helper.cpp
index 3e4d1507dbc..3c1ad114976 100644
--- a/src/mongo/db/s/move_timing_helper.cpp
+++ b/src/mongo/db/s/move_timing_helper.cpp
@@ -46,8 +46,8 @@ MoveTimingHelper::MoveTimingHelper(OperationContext* txn,
                                    const BSONObj& max,
                                    int totalNumSteps,
                                    std::string* cmdErrmsg,
-                                   const std::string& toShard,
-                                   const std::string& fromShard)
+                                   const ShardId& toShard,
+                                   const ShardId& fromShard)
     : _txn(txn),
       _where(where),
       _ns(ns),
@@ -64,12 +64,12 @@ MoveTimingHelper::~MoveTimingHelper() {
     // even if logChange doesn't throw, bson does
     // sigh
     try {
-        if (!_to.empty()) {
-            _b.append("to", _to);
+        if (_to.isValid()) {
+            _b.append("to", _to.toString());
         }
 
-        if (!_from.empty()) {
-            _b.append("from", _from);
+        if (_from.isValid()) {
+            _b.append("from", _from.toString());
         }
 
         if (_nextStep != _totalNumSteps) {
diff --git a/src/mongo/db/s/move_timing_helper.h b/src/mongo/db/s/move_timing_helper.h
index fc799ca1d6d..bc1f2644ac7 100644
--- a/src/mongo/db/s/move_timing_helper.h
+++ b/src/mongo/db/s/move_timing_helper.h
@@ -31,6 +31,7 @@
 #include <string>
 
 #include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/s/shard_id.h"
 #include "mongo/util/timer.h"
 
 namespace mongo {
@@ -47,8 +48,8 @@ public:
                      const BSONObj& max,
                      int totalNumSteps,
                      std::string* cmdErrmsg,
-                     const std::string& toShard,
-                     const std::string& fromShard);
+                     const ShardId& toShard,
+                     const ShardId& fromShard);
     ~MoveTimingHelper();
 
     void done(int step);
@@ -60,8 +61,8 @@ private:
     OperationContext* const _txn;
     const std::string _where;
     const std::string _ns;
-    const std::string _to;
-    const std::string _from;
+    const ShardId _to;
+    const ShardId _from;
     const int _totalNumSteps;
     const std::string* _cmdErrmsg;
 
diff --git a/src/mongo/db/s/start_chunk_clone_request.cpp b/src/mongo/db/s/start_chunk_clone_request.cpp
index fbeb861ede7..9aa27ba5fc9 100644
--- a/src/mongo/db/s/start_chunk_clone_request.cpp
+++ b/src/mongo/db/s/start_chunk_clone_request.cpp
@@ -33,6 +33,7 @@
 #include "mongo/base/status_with.h"
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/bson/util/bson_extract.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 namespace {
@@ -160,7 +161,7 @@ void StartChunkCloneRequest::appendAsCommand(
     const MigrationSessionId& sessionId,
     const ConnectionString& configServerConnectionString,
     const ConnectionString& fromShardConnectionString,
-    const std::string& toShardId,
+    const ShardId& toShardId,
     const BSONObj& chunkMinKey,
     const BSONObj& chunkMaxKey,
     const BSONObj& shardKeyPattern,
@@ -173,7 +174,7 @@ void StartChunkCloneRequest::appendAsCommand(
     sessionId.append(builder);
     builder->append(kConfigServerConnectionString, configServerConnectionString.toString());
     builder->append(kFromShardConnectionString, fromShardConnectionString.toString());
-    builder->append(kToShardId, toShardId);
+    builder->append(kToShardId, toShardId.toString());
     builder->append(kChunkMinKey, chunkMinKey);
     builder->append(kChunkMaxKey, chunkMaxKey);
     builder->append(kShardKeyPattern, shardKeyPattern);
diff --git a/src/mongo/db/s/start_chunk_clone_request.h b/src/mongo/db/s/start_chunk_clone_request.h
index ce66f7f2b12..8a7b43d5f27 100644
--- a/src/mongo/db/s/start_chunk_clone_request.h
+++ b/src/mongo/db/s/start_chunk_clone_request.h
@@ -40,7 +40,7 @@ namespace mongo {
 class BSONObjBuilder;
 template <typename T>
 class StatusWith;
-
+class ShardId;
 /**
  * Parses the arguments for a start chunk clone operation.
  */
@@ -62,7 +62,7 @@ public:
                                 const MigrationSessionId& sessionId,
                                 const ConnectionString& configServerConnectionString,
                                 const ConnectionString& fromShardConnectionString,
-                                const std::string& toShardId,
+                                const ShardId& toShardId,
                                 const BSONObj& chunkMinKey,
                                 const BSONObj& chunkMaxKey,
                                 const BSONObj& shardKeyPattern,
diff --git a/src/mongo/db/s/start_chunk_clone_request_test.cpp b/src/mongo/db/s/start_chunk_clone_request_test.cpp
index 2b977178781..107c5628580 100644
--- a/src/mongo/db/s/start_chunk_clone_request_test.cpp
+++ b/src/mongo/db/s/start_chunk_clone_request_test.cpp
@@ -33,6 +33,7 @@
 #include "mongo/base/status_with.h"
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/db/jsobj.h"
+#include "mongo/s/shard_id.h"
 #include "mongo/unittest/unittest.h"
 
 namespace mongo {
@@ -51,7 +52,7 @@ TEST(StartChunkCloneRequest, CreateAsCommandComplete) {
         sessionId,
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
         assertGet(ConnectionString::parse("TestDonorRS/Donor1:12345,Donor2:12345,Donor3:12345")),
-        "shard0002",
+        ShardId("shard0002"),
         BSON("Key" << -100),
         BSON("Key" << 100),
         BSON("Key" << 1),
diff --git a/src/mongo/s/SConscript b/src/mongo/s/SConscript
index 3d047de7734..c4411742da5 100644
--- a/src/mongo/s/SConscript
+++ b/src/mongo/s/SConscript
@@ -33,6 +33,16 @@ env.Library(
 
 # Functionality shared between mongod and mongos
 env.Library(
+    target='shard_id',
+    source=[
+        'shard_id.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+    ]
+)
+
+env.Library(
     target='common',
     source=[
         'catalog/mongo_version_range.cpp',
@@ -60,6 +70,7 @@ env.Library(
         'shard_key_pattern.cpp',
     ],
     LIBDEPS=[
+        'shard_id',
         '$BUILD_DIR/mongo/client/connection_string',
         '$BUILD_DIR/mongo/db/common',
         '$BUILD_DIR/mongo/db/matcher/expressions',
@@ -99,6 +110,16 @@ env.Library(
 )
 
 env.CppUnitTest(
+    target='shard_id_test',
+    source=[
+        'shard_id_test.cpp',
+    ],
+    LIBDEPS=[
+        'common',
+    ]
+)
+
+env.CppUnitTest(
     target='sharding_common_test',
     source=[
         'catalog/type_changelog_test.cpp',
@@ -116,6 +137,7 @@ env.CppUnitTest(
         'move_chunk_request_test.cpp',
         'set_shard_version_request_test.cpp',
         'shard_key_pattern_test.cpp',
+#        'shard_id_test.cpp',
     ],
     LIBDEPS=[
         '$BUILD_DIR/mongo/db/query/query_test_service_context',
diff --git a/src/mongo/s/balancer/balancer.cpp b/src/mongo/s/balancer/balancer.cpp
index c751467ea25..c75b4d3b93b 100644
--- a/src/mongo/s/balancer/balancer.cpp
+++ b/src/mongo/s/balancer/balancer.cpp
@@ -600,7 +600,7 @@ bool Balancer::_checkOIDs(OperationContext* txn) {
     shardingContext->shardRegistry()->getAllShardIds(&all);
 
     // map of OID machine ID => shardId
-    map<int, string> oids;
+    map<int, ShardId> oids;
 
     for (const ShardId& shardId : all) {
         const auto s = shardingContext->shardRegistry()->getShard(txn, shardId);
diff --git a/src/mongo/s/balancer/balancer_chunk_selection_policy_impl.cpp b/src/mongo/s/balancer/balancer_chunk_selection_policy_impl.cpp
index e2a00e9034f..f95158b3039 100644
--- a/src/mongo/s/balancer/balancer_chunk_selection_policy_impl.cpp
+++ b/src/mongo/s/balancer/balancer_chunk_selection_policy_impl.cpp
@@ -210,7 +210,7 @@ BalancerChunkSelectionPolicyImpl::selectSpecificChunkToMove(OperationContext* tx
 
     DistributionStatus distStatus(shardStatsStatus.getValue(), shardToChunksMap);
     const ShardId newShardId(distStatus.getBestReceieverShard(tagForChunkStatus.getValue()));
-    if (newShardId.empty() || newShardId == chunk.getShard()) {
+    if (!newShardId.isValid() || newShardId == chunk.getShard()) {
         return boost::optional<MigrateInfo>();
     }
 
diff --git a/src/mongo/s/balancer/balancer_policy.cpp b/src/mongo/s/balancer/balancer_policy.cpp
index f588f089702..b679858e2d0 100644
--- a/src/mongo/s/balancer/balancer_policy.cpp
+++ b/src/mongo/s/balancer/balancer_policy.cpp
@@ -118,8 +118,8 @@ Status DistributionStatus::isShardSuitableReceiver(const ClusterStatistics::Shar
     return Status::OK();
 }
 
-string DistributionStatus::getBestReceieverShard(const string& tag) const {
-    string best;
+ShardId DistributionStatus::getBestReceieverShard(const string& tag) const {
+    ShardId best;
     unsigned minChunks = numeric_limits<unsigned>::max();
 
     for (const auto& stat : _shardInfo) {
@@ -143,8 +143,8 @@ string DistributionStatus::getBestReceieverShard(const string& tag) const {
     return best;
 }
 
-string DistributionStatus::getMostOverloadedShard(const string& tag) const {
-    string worst;
+ShardId DistributionStatus::getMostOverloadedShard(const string& tag) const {
+    ShardId worst;
     unsigned maxChunks = 0;
 
     for (const auto& stat : _shardInfo) {
@@ -274,7 +274,7 @@ MigrateInfo* BalancerPolicy::balance(const string& ns,
                 string tag = distribution.getTagForChunk(chunkToMove);
                 const ShardId to = distribution.getBestReceieverShard(tag);
 
-                if (to.size() == 0) {
+                if (!to.isValid()) {
                     warning() << "want to move chunk: " << chunkToMove << "(" << tag << ") "
                               << "from " << stat.shardId << " but can't find anywhere to put it";
                     continue;
@@ -313,7 +313,7 @@ MigrateInfo* BalancerPolicy::balance(const string& ns,
                 }
 
                 const ShardId to = distribution.getBestReceieverShard(tag);
-                if (to.size() == 0) {
+                if (!to.isValid()) {
                     log() << "no where to put it :(";
                     continue;
                 }
@@ -349,15 +349,15 @@ MigrateInfo* BalancerPolicy::balance(const string& ns,
         string tag = tags[i];
 
         const ShardId from = distribution.getMostOverloadedShard(tag);
-        if (from.size() == 0)
+        if (!from.isValid())
             continue;
 
         unsigned max = distribution.numberOfChunksInShardWithTag(from, tag);
         if (max == 0)
             continue;
 
-        string to = distribution.getBestReceieverShard(tag);
-        if (to.size() == 0) {
+        ShardId to = distribution.getBestReceieverShard(tag);
+        if (!to.isValid()) {
             log() << "no available shards to take chunks for tag [" << tag << "]";
             return NULL;
         }
diff --git a/src/mongo/s/balancer/balancer_policy.h b/src/mongo/s/balancer/balancer_policy.h
index 428349098a1..8717aca4045 100644
--- a/src/mongo/s/balancer/balancer_policy.h
+++ b/src/mongo/s/balancer/balancer_policy.h
@@ -95,13 +95,13 @@ public:
      * @param forTag "" if you don't care, or a tag
      * @return shard best suited to receive a chunk
      */
-    std::string getBestReceieverShard(const std::string& tag) const;
+    ShardId getBestReceieverShard(const std::string& tag) const;
 
     /**
      * @return the shard with the most chunks
      *         based on # of chunks with the given tag
      */
-    std::string getMostOverloadedShard(const std::string& forTag) const;
+    ShardId getMostOverloadedShard(const std::string& forTag) const;
 
 
     // ---- basic accessors, counters, etc...
diff --git a/src/mongo/s/balancer/balancer_policy_tests.cpp b/src/mongo/s/balancer/balancer_policy_tests.cpp
index b0ba5c29ce3..95746bae017 100644
--- a/src/mongo/s/balancer/balancer_policy_tests.cpp
+++ b/src/mongo/s/balancer/balancer_policy_tests.cpp
@@ -66,7 +66,7 @@ TEST(BalancerPolicyTests, BalanceNormalTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << BSON("$maxKey" << 1)));
         chunk.setMax(BSON("x" << 49));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -74,17 +74,17 @@ TEST(BalancerPolicyTests, BalanceNormalTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 49));
         chunk.setMax(BSON("x" << BSON("$maxKey" << 1)));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
-    chunkMap["shard0"] = chunks;
-    chunkMap["shard1"] = vector<ChunkType>();
+    chunkMap[ShardId("shard0")] = chunks;
+    chunkMap[ShardId("shard1")] = vector<ChunkType>();
 
     // No limits
     DistributionStatus status(
-        {ShardStatistics("shard0", 0, 2, false, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard1", 0, 0, false, emptyTagSet, emptyShardVersion)},
+        {ShardStatistics(ShardId("shard0"), 0, 2, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 0, false, emptyTagSet, emptyShardVersion)},
         chunkMap);
 
     std::unique_ptr<MigrateInfo> c(BalancerPolicy::balance("ns", status, 1));
@@ -101,7 +101,7 @@ TEST(BalancerPolicyTests, BalanceJumbo) {
         chunk.setMin(BSON("x" << BSON("$maxKey" << 1)));
         chunk.setMax(BSON("x" << 10));
         chunk.setJumbo(true);
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -110,7 +110,7 @@ TEST(BalancerPolicyTests, BalanceJumbo) {
         chunk.setMin(BSON("x" << 10));
         chunk.setMax(BSON("x" << 20));
         chunk.setJumbo(true);
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -118,7 +118,7 @@ TEST(BalancerPolicyTests, BalanceJumbo) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 20));
         chunk.setMax(BSON("x" << 30));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -127,7 +127,7 @@ TEST(BalancerPolicyTests, BalanceJumbo) {
         chunk.setMin(BSON("x" << 30));
         chunk.setMax(BSON("x" << 40));
         chunk.setJumbo(true);
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -135,17 +135,17 @@ TEST(BalancerPolicyTests, BalanceJumbo) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 40));
         chunk.setMax(BSON("x" << BSON("$maxKey" << 1)));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
-    chunkMap["shard0"] = chunks;
-    chunkMap["shard1"] = vector<ChunkType>();
+    chunkMap[ShardId("shard0")] = chunks;
+    chunkMap[ShardId("shard1")] = vector<ChunkType>();
 
     // No limits
     DistributionStatus status(
-        {ShardStatistics("shard0", 0, 2, false, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard1", 0, 0, false, emptyTagSet, emptyShardVersion)},
+        {ShardStatistics(ShardId("shard0"), 0, 2, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 0, false, emptyTagSet, emptyShardVersion)},
         chunkMap);
     std::unique_ptr<MigrateInfo> c(BalancerPolicy::balance("ns", status, 1));
 
@@ -161,7 +161,7 @@ TEST(BalanceNormalTests, BalanceDrainingTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << BSON("$maxKey" << 1)));
         chunk.setMax(BSON("x" << 49));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -169,23 +169,23 @@ TEST(BalanceNormalTests, BalanceDrainingTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 49));
         chunk.setMax(BSON("x" << BSON("$maxKey" << 1)));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
-    chunkMap["shard0"] = chunks;
-    chunkMap["shard1"] = vector<ChunkType>();
+    chunkMap[ShardId("shard0")] = chunks;
+    chunkMap[ShardId("shard1")] = vector<ChunkType>();
 
     // shard0 is draining
     DistributionStatus status(
-        {ShardStatistics("shard0", 0, 2, true, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard1", 0, 0, false, emptyTagSet, emptyShardVersion)},
+        {ShardStatistics(ShardId("shard0"), 0, 2, true, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 0, false, emptyTagSet, emptyShardVersion)},
         chunkMap);
     std::unique_ptr<MigrateInfo> c(BalancerPolicy::balance("ns", status, 0));
 
     ASSERT(c);
-    ASSERT_EQUALS(c->to, "shard1");
-    ASSERT_EQUALS(c->from, "shard0");
+    ASSERT_EQUALS(c->to, ShardId("shard1"));
+    ASSERT_EQUALS(c->from, ShardId("shard0"));
     ASSERT(!c->minKey.isEmpty());
 }
 
@@ -197,7 +197,7 @@ TEST(BalancerPolicyTests, BalanceEndedDrainingTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << BSON("$maxKey" << 1)));
         chunk.setMax(BSON("x" << 49));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
@@ -205,17 +205,17 @@ TEST(BalancerPolicyTests, BalanceEndedDrainingTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 49));
         chunk.setMax(BSON("x" << BSON("$maxKey" << 1)));
-        chunk.setShard("shard0");
+        chunk.setShard(ShardId("shard0"));
         chunks.push_back(chunk);
     }
 
-    chunkMap["shard0"] = chunks;
-    chunkMap["shard1"] = vector<ChunkType>();
+    chunkMap[ShardId("shard0")] = chunks;
+    chunkMap[ShardId("shard1")] = vector<ChunkType>();
 
     // shard1 is draining
     DistributionStatus status(
-        {ShardStatistics("shard0", 0, 2, false, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard1", 0, 0, true, emptyTagSet, emptyShardVersion)},
+        {ShardStatistics(ShardId("shard0"), 0, 2, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 0, true, emptyTagSet, emptyShardVersion)},
         chunkMap);
     std::unique_ptr<MigrateInfo> c(BalancerPolicy::balance("ns", status, 0));
 
@@ -230,7 +230,7 @@ TEST(BalancerPolicyTests, BalanceImpasseTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << BSON("$maxKey" << 1)));
         chunk.setMax(BSON("x" << 49));
-        chunk.setShard("shard1");
+        chunk.setShard(ShardId("shard1"));
         chunks.push_back(chunk);
     }
 
@@ -238,19 +238,19 @@ TEST(BalancerPolicyTests, BalanceImpasseTest) {
         ChunkType chunk;
         chunk.setMin(BSON("x" << 49));
         chunk.setMax(BSON("x" << BSON("$maxKey" << 1)));
-        chunk.setShard("shard1");
+        chunk.setShard(ShardId("shard1"));
         chunks.push_back(chunk);
     }
 
-    chunkMap["shard0"] = vector<ChunkType>();
-    chunkMap["shard1"] = chunks;
-    chunkMap["shard2"] = vector<ChunkType>();
+    chunkMap[ShardId("shard0")] = vector<ChunkType>();
+    chunkMap[ShardId("shard1")] = chunks;
+    chunkMap[ShardId("shard2")] = vector<ChunkType>();
 
     // shard0 is draining, shard1 is maxed out, shard2 has writebacks pending
     DistributionStatus status(
-        {ShardStatistics("shard0", 0, 2, true, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard1", 1, 1, false, emptyTagSet, emptyShardVersion),
-         ShardStatistics("shard2", 0, 1, true, emptyTagSet, emptyShardVersion)},
+        {ShardStatistics(ShardId("shard0"), 0, 2, true, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 1, 1, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard2"), 0, 1, true, emptyTagSet, emptyShardVersion)},
         chunkMap);
     std::unique_ptr<MigrateInfo> c(BalancerPolicy::balance("ns", status, 0));
 
@@ -312,14 +312,15 @@ TEST(BalancerPolicyTests, MultipleDraining) {
     addShard(chunks, 10, false);
     addShard(chunks, 5, true);
 
-    DistributionStatus d({ShardStatistics("shard0", 0, 5, true, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard1", 0, 5, true, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard2", 0, 5, false, emptyTagSet, emptyShardVersion)},
-                         chunks);
+    DistributionStatus d(
+        {ShardStatistics(ShardId("shard0"), 0, 5, true, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 5, true, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard2"), 0, 5, false, emptyTagSet, emptyShardVersion)},
+        chunks);
     std::unique_ptr<MigrateInfo> m(BalancerPolicy::balance("ns", d, 0));
 
     ASSERT(m);
-    ASSERT_EQUALS("shard2", m->to);
+    ASSERT_EQUALS(ShardId("shard2"), m->to);
 }
 
 
@@ -330,10 +331,11 @@ TEST(BalancerPolicyTests, TagsDraining) {
     addShard(chunks, 5, true);
 
     while (true) {
-        DistributionStatus d({ShardStatistics("shard0", 0, 5, false, {"a"}, emptyShardVersion),
-                              ShardStatistics("shard1", 0, 5, true, {"a", "b"}, emptyShardVersion),
-                              ShardStatistics("shard2", 0, 5, false, {"b"}, emptyShardVersion)},
-                             chunks);
+        DistributionStatus d(
+            {ShardStatistics(ShardId("shard0"), 0, 5, false, {"a"}, emptyShardVersion),
+             ShardStatistics(ShardId("shard1"), 0, 5, true, {"a", "b"}, emptyShardVersion),
+             ShardStatistics(ShardId("shard2"), 0, 5, false, {"b"}, emptyShardVersion)},
+            chunks);
 
         d.addTagRange(TagRange(BSON("x" << -1), BSON("x" << 7), "a"));
         d.addTagRange(TagRange(BSON("x" << 7), BSON("x" << 1000), "b"));
@@ -344,17 +346,17 @@ TEST(BalancerPolicyTests, TagsDraining) {
         }
 
         if (m->minKey["x"].numberInt() < 7) {
-            ASSERT_EQUALS("shard0", m->to);
+            ASSERT_EQUALS(ShardId("shard0"), m->to);
         } else {
-            ASSERT_EQUALS("shard2", m->to);
+            ASSERT_EQUALS(ShardId("shard2"), m->to);
         }
 
         moveChunk(chunks, m.get());
     }
 
-    ASSERT_EQUALS(7U, chunks["shard0"].size());
-    ASSERT_EQUALS(0U, chunks["shard1"].size());
-    ASSERT_EQUALS(8U, chunks["shard2"].size());
+    ASSERT_EQUALS(7U, chunks[ShardId("shard0")].size());
+    ASSERT_EQUALS(0U, chunks[ShardId("shard1")].size());
+    ASSERT_EQUALS(8U, chunks[ShardId("shard2")].size());
 }
 
 
@@ -366,9 +368,9 @@ TEST(BalancerPolicyTests, TagsPolicyChange) {
 
     while (true) {
         DistributionStatus d(
-            {ShardStatistics("shard0", 0, 5, false, {"a"}, emptyShardVersion),
-             ShardStatistics("shard1", 0, 5, false, {"a"}, emptyShardVersion),
-             ShardStatistics("shard2", 0, 5, false, emptyTagSet, emptyShardVersion)},
+            {ShardStatistics(ShardId("shard0"), 0, 5, false, {"a"}, emptyShardVersion),
+             ShardStatistics(ShardId("shard1"), 0, 5, false, {"a"}, emptyShardVersion),
+             ShardStatistics(ShardId("shard2"), 0, 5, false, emptyTagSet, emptyShardVersion)},
             chunks);
         d.addTagRange(TagRange(BSON("x" << -1), BSON("x" << 1000), "a"));
 
@@ -380,12 +382,12 @@ TEST(BalancerPolicyTests, TagsPolicyChange) {
         moveChunk(chunks, m.get());
     }
 
-    const size_t shard0Size = chunks["shard0"].size();
-    const size_t shard1Size = chunks["shard1"].size();
+    const size_t shard0Size = chunks[ShardId("shard0")].size();
+    const size_t shard1Size = chunks[ShardId("shard1")].size();
 
     ASSERT_EQUALS(15U, shard0Size + shard1Size);
     ASSERT(shard0Size == 7U || shard0Size == 8U);
-    ASSERT_EQUALS(0U, chunks["shard2"].size());
+    ASSERT_EQUALS(0U, chunks[ShardId("shard2")].size());
 }
 
 
@@ -457,15 +459,16 @@ TEST(BalancerPolicyTests, MaxSizeRespect) {
 
     // Note that maxSize of shard0 is 1, and it is therefore overloaded with currSize = 3.
     // Other shards have maxSize = 0 = unset.
-    DistributionStatus d({ShardStatistics("shard0", 1, 3, false, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard1", 0, 4, false, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard2", 0, 6, false, emptyTagSet, emptyShardVersion)},
-                         chunks);
+    DistributionStatus d(
+        {ShardStatistics(ShardId("shard0"), 1, 3, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 4, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard2"), 0, 6, false, emptyTagSet, emptyShardVersion)},
+        chunks);
     std::unique_ptr<MigrateInfo> m(BalancerPolicy::balance("ns", d, 0));
 
     ASSERT(m);
-    ASSERT_EQUALS("shard2", m->from);
-    ASSERT_EQUALS("shard1", m->to);
+    ASSERT_EQUALS(ShardId("shard2"), m->from);
+    ASSERT_EQUALS(ShardId("shard1"), m->to);
 }
 
 /**
@@ -482,10 +485,11 @@ TEST(BalancerPolicyTests, MaxSizeNoDrain) {
 
     // Note that maxSize of shard0 is 1, and it is therefore overloaded with currSize = 4. Other
     // shards have maxSize = 0 = unset.
-    DistributionStatus d({ShardStatistics("shard0", 1, 4, false, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard1", 0, 4, false, emptyTagSet, emptyShardVersion),
-                          ShardStatistics("shard2", 0, 4, false, emptyTagSet, emptyShardVersion)},
-                         chunks);
+    DistributionStatus d(
+        {ShardStatistics(ShardId("shard0"), 1, 4, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard1"), 0, 4, false, emptyTagSet, emptyShardVersion),
+         ShardStatistics(ShardId("shard2"), 0, 4, false, emptyTagSet, emptyShardVersion)},
+        chunks);
     std::unique_ptr<MigrateInfo> m(BalancerPolicy::balance("ns", d, 0));
 
     ASSERT(!m);
@@ -519,7 +523,7 @@ TEST(BalancerPolicyTests, Simulation) {
         ShardToChunksMap chunks;
         vector<ShardStatistics> shards;
 
-        map<string, int> expected;
+        map<ShardId, int> expected;
 
         for (int i = 0; i < numShards; i++) {
             int numShardChunks = rng.nextInt32(100);
@@ -527,17 +531,17 @@ TEST(BalancerPolicyTests, Simulation) {
             bool maxed = i >= 2 && i < 4;
 
             if (draining) {
-                expected[str::stream() << "shard" << i] = 0;
+                expected[ShardId(str::stream() << "shard" << i)] = 0;
             }
 
             if (maxed) {
-                expected[str::stream() << "shard" << i] = numShardChunks + 1;
+                expected[ShardId(str::stream() << "shard" << i)] = numShardChunks + 1;
             }
 
             addShard(chunks, numShardChunks, false);
             numChunks += numShardChunks;
 
-            shards.emplace_back(str::stream() << "shard" << i,
+            shards.emplace_back(ShardId(str::stream() << "shard" << i),
                                 maxed ? numShardChunks + 1 : 0,
                                 numShardChunks,
                                 draining,
@@ -576,7 +580,7 @@ TEST(BalancerPolicyTests, Simulation) {
             // Cast the size once and use it from here in order to avoid typecast errors
             const int shardCurrSizeMB = static_cast<int>(stat.currSizeMB);
 
-            map<string, int>::iterator expectedIt = expected.find(stat.shardId);
+            map<ShardId, int>::iterator expectedIt = expected.find(stat.shardId);
 
             if (expectedIt == expected.end()) {
                 const bool isInRange =
diff --git a/src/mongo/s/balancer/cluster_statistics.cpp b/src/mongo/s/balancer/cluster_statistics.cpp
index 0c66348ef36..c951c865ce0 100644
--- a/src/mongo/s/balancer/cluster_statistics.cpp
+++ b/src/mongo/s/balancer/cluster_statistics.cpp
@@ -64,7 +64,7 @@ bool ClusterStatistics::ShardStatistics::isSizeMaxed() const {
 
 BSONObj ClusterStatistics::ShardStatistics::toBSON() const {
     BSONObjBuilder builder;
-    builder.append("id", shardId);
+    builder.append("id", shardId.toString());
     builder.append("maxSizeMB", static_cast<long long>(maxSizeMB));
     builder.append("currSizeMB", static_cast<long long>(currSizeMB));
     builder.append("draining", isDraining);
diff --git a/src/mongo/s/balancer/cluster_statistics_test.cpp b/src/mongo/s/balancer/cluster_statistics_test.cpp
index 4fe4f0b27e5..c9115b6dafd 100644
--- a/src/mongo/s/balancer/cluster_statistics_test.cpp
+++ b/src/mongo/s/balancer/cluster_statistics_test.cpp
@@ -39,9 +39,12 @@ using ShardStatistics = ClusterStatistics::ShardStatistics;
 const auto emptyTagSet = std::set<std::string>();
 
 TEST(ShardStatistics, SizeMaxedTest) {
-    ASSERT(!ShardStatistics("TestShardId", 0, 0, false, emptyTagSet, "3.2.0").isSizeMaxed());
-    ASSERT(!ShardStatistics("TestShardId", 100LL, 80LL, false, emptyTagSet, "3.2.0").isSizeMaxed());
-    ASSERT(ShardStatistics("TestShardId", 100LL, 110LL, false, emptyTagSet, "3.2.0").isSizeMaxed());
+    ASSERT(
+        !ShardStatistics(ShardId("TestShardId"), 0, 0, false, emptyTagSet, "3.2.0").isSizeMaxed());
+    ASSERT(!ShardStatistics(ShardId("TestShardId"), 100LL, 80LL, false, emptyTagSet, "3.2.0")
+                .isSizeMaxed());
+    ASSERT(ShardStatistics(ShardId("TestShardId"), 100LL, 110LL, false, emptyTagSet, "3.2.0")
+               .isSizeMaxed());
 }
 
 }  // namespace
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_add_shard_test.cpp b/src/mongo/s/catalog/replset/sharding_catalog_add_shard_test.cpp
index 62a79a0e37b..a09fe9834b4 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_add_shard_test.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_add_shard_test.cpp
@@ -345,7 +345,7 @@ TEST_F(AddShardTest, Standalone) {
     {
         DatabaseType dbTestDB1;
         dbTestDB1.setName("TestDB1");
-        dbTestDB1.setPrimary("StandaloneShard");
+        dbTestDB1.setPrimary(ShardId("StandaloneShard"));
         dbTestDB1.setSharded(false);
 
         expectDatabaseUpdate(dbTestDB1);
@@ -354,7 +354,7 @@ TEST_F(AddShardTest, Standalone) {
     {
         DatabaseType dbTestDB2;
         dbTestDB2.setName("TestDB2");
-        dbTestDB2.setPrimary("StandaloneShard");
+        dbTestDB2.setPrimary(ShardId("StandaloneShard"));
         dbTestDB2.setSharded(false);
 
         expectDatabaseUpdate(dbTestDB2);
@@ -445,7 +445,7 @@ TEST_F(AddShardTest, StandaloneGenerateName) {
     {
         DatabaseType dbTestDB1;
         dbTestDB1.setName("TestDB1");
-        dbTestDB1.setPrimary("shard0006");
+        dbTestDB1.setPrimary(ShardId("shard0006"));
         dbTestDB1.setSharded(false);
 
         expectDatabaseUpdate(dbTestDB1);
@@ -454,7 +454,7 @@ TEST_F(AddShardTest, StandaloneGenerateName) {
     {
         DatabaseType dbTestDB2;
         dbTestDB2.setName("TestDB2");
-        dbTestDB2.setPrimary("shard0006");
+        dbTestDB2.setPrimary(ShardId("shard0006"));
         dbTestDB2.setSharded(false);
 
         expectDatabaseUpdate(dbTestDB2);
@@ -829,7 +829,7 @@ TEST_F(AddShardTest, ShardContainsExistingDatabase) {
 
     DatabaseType existing;
     existing.setName("existing");
-    existing.setPrimary("existingShard");
+    existing.setPrimary(ShardId("existingShard"));
     expectGetDatabase("existing", existing);
 
     future.timed_get(kFutureTimeout);
@@ -953,7 +953,7 @@ TEST_F(AddShardTest, SuccessfullyAddReplicaSet) {
     // Add the existing database from the newly added shard
     DatabaseType shardDB;
     shardDB.setName("shardDB");
-    shardDB.setPrimary(expectedShardName);
+    shardDB.setPrimary(ShardId(expectedShardName));
     shardDB.setSharded(false);
 
     expectDatabaseUpdate(shardDB);
@@ -1014,7 +1014,7 @@ TEST_F(AddShardTest, AddShardSucceedsEvenIfAddingDBsFromNewShardFails) {
     // Add the existing database from the newly added shard
     DatabaseType shardDB;
     shardDB.setName("shardDB");
-    shardDB.setPrimary(expectedShardName);
+    shardDB.setPrimary(ShardId(expectedShardName));
     shardDB.setSharded(false);
 
     // Ensure that even if upserting the database discovered on the shard fails, the addShard
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp b/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp
index 71c060df46f..caf410e35a3 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp
@@ -471,7 +471,7 @@ Status ShardingCatalogClientImpl::shardCollection(OperationContext* txn,
         {
             BSONArrayBuilder initialShards(collectionDetail.subarrayStart("initShards"));
             for (const ShardId& shardId : initShardIds) {
-                initialShards.append(shardId);
+                initialShards.append(shardId.toString());
             }
         }
 
@@ -527,8 +527,9 @@ Status ShardingCatalogClientImpl::shardCollection(OperationContext* txn,
 }
 
 StatusWith<ShardDrainingStatus> ShardingCatalogClientImpl::removeShard(OperationContext* txn,
-                                                                       const std::string& name) {
+                                                                       const ShardId& shardId) {
     // Check preconditions for removing the shard
+    string name = shardId.toString();
     auto countStatus = _runCountCommandOnConfig(
         txn,
         NamespaceString(ShardType::ConfigNS),
@@ -634,7 +635,7 @@ StatusWith<repl::OpTimeWith<DatabaseType>> ShardingCatalogClientImpl::getDatabas
         DatabaseType dbt;
         dbt.setName(dbName);
         dbt.setSharded(false);
-        dbt.setPrimary("config");
+        dbt.setPrimary(ShardId("config"));
 
         return repl::OpTimeWith<DatabaseType>(dbt);
     }
@@ -936,12 +937,12 @@ StatusWith<BSONObj> ShardingCatalogClientImpl::getGlobalSettings(OperationContex
 }
 
 Status ShardingCatalogClientImpl::getDatabasesForShard(OperationContext* txn,
-                                                       const string& shardName,
+                                                       const ShardId& shardId,
                                                        vector<string>* dbs) {
     auto findStatus = _exhaustiveFindOnConfig(txn,
                                               kConfigReadSelector,
                                               NamespaceString(DatabaseType::ConfigNS),
-                                              BSON(DatabaseType::primary(shardName)),
+                                              BSON(DatabaseType::primary(shardId.toString())),
                                               BSONObj(),
                                               boost::none);  // no limit
     if (!findStatus.isOK()) {
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_client_impl.h b/src/mongo/s/catalog/replset/sharding_catalog_client_impl.h
index 48df7545263..a31dac7b353 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_client_impl.h
+++ b/src/mongo/s/catalog/replset/sharding_catalog_client_impl.h
@@ -95,7 +95,7 @@ public:
                            const std::set<ShardId>& initShardsIds) override;
 
     StatusWith<ShardDrainingStatus> removeShard(OperationContext* txn,
-                                                const std::string& name) override;
+                                                const ShardId& name) override;
 
     StatusWith<repl::OpTimeWith<DatabaseType>> getDatabase(OperationContext* txn,
                                                            const std::string& dbName) override;
@@ -111,7 +111,7 @@ public:
     Status dropCollection(OperationContext* txn, const NamespaceString& ns) override;
 
     Status getDatabasesForShard(OperationContext* txn,
-                                const std::string& shardName,
+                                const ShardId& shardName,
                                 std::vector<std::string>* dbs) override;
 
     Status getChunks(OperationContext* txn,
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_test.cpp b/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
index a175821900a..05787798d19 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
@@ -155,7 +155,7 @@ TEST_F(ShardingCatalogClientTest, GetDatabaseExisting) {
 
     DatabaseType expectedDb;
     expectedDb.setName("bigdata");
-    expectedDb.setPrimary("shard0000");
+    expectedDb.setPrimary(ShardId("shard0000"));
     expectedDb.setSharded(true);
 
     const OpTime newOpTime(Timestamp(7, 6), 5);
@@ -198,7 +198,7 @@ TEST_F(ShardingCatalogClientTest, GetDatabaseStaleSecondaryRetrySuccess) {
 
     DatabaseType expectedDb;
     expectedDb.setName("bigdata");
-    expectedDb.setPrimary("shard0000");
+    expectedDb.setPrimary(ShardId("shard0000"));
     expectedDb.setSharded(true);
 
     auto future = launchAsync([this, &expectedDb] {
@@ -453,14 +453,14 @@ TEST_F(ShardingCatalogClientTest, GetChunksForNSWithSortAndLimit) {
     chunkA.setMin(BSON("a" << 1));
     chunkA.setMax(BSON("a" << 100));
     chunkA.setVersion({1, 2, oid});
-    chunkA.setShard("shard0000");
+    chunkA.setShard(ShardId("shard0000"));
 
     ChunkType chunkB;
     chunkB.setNS("TestDB.TestColl");
     chunkB.setMin(BSON("a" << 100));
     chunkB.setMax(BSON("a" << 200));
     chunkB.setVersion({3, 4, oid});
-    chunkB.setShard("shard0001");
+    chunkB.setShard(ShardId("shard0001"));
 
     ChunkVersion queryChunkVersion({1, 2, oid});
 
@@ -581,7 +581,7 @@ TEST_F(ShardingCatalogClientTest, GetChunksForNSInvalidChunk) {
         chunkA.setMin(BSON("a" << 1));
         chunkA.setMax(BSON("a" << 100));
         chunkA.setVersion({1, 2, OID::gen()});
-        chunkA.setShard("shard0000");
+        chunkA.setShard(ShardId("shard0000"));
 
         ChunkType chunkB;
         chunkB.setNS("TestDB.TestColl");
@@ -1019,16 +1019,16 @@ TEST_F(ShardingCatalogClientTest, GetDatabasesForShardValid) {
 
     DatabaseType dbt1;
     dbt1.setName("db1");
-    dbt1.setPrimary("shard0000");
+    dbt1.setPrimary(ShardId("shard0000"));
 
     DatabaseType dbt2;
     dbt2.setName("db2");
-    dbt2.setPrimary("shard0000");
+    dbt2.setPrimary(ShardId("shard0000"));
 
     auto future = launchAsync([this] {
         vector<string> dbs;
         const auto status =
-            catalogClient()->getDatabasesForShard(operationContext(), "shard0000", &dbs);
+            catalogClient()->getDatabasesForShard(operationContext(), ShardId("shard0000"), &dbs);
 
         ASSERT_OK(status);
         return dbs;
@@ -1043,7 +1043,7 @@ TEST_F(ShardingCatalogClientTest, GetDatabasesForShardValid) {
         auto query = assertGet(QueryRequest::makeFromFindCommand(nss, request.cmdObj, false));
 
         ASSERT_EQ(query->ns(), DatabaseType::ConfigNS);
-        ASSERT_EQ(query->getFilter(), BSON(DatabaseType::primary(dbt1.getPrimary())));
+        ASSERT_EQ(query->getFilter(), BSON(DatabaseType::primary(dbt1.getPrimary().toString())));
         ASSERT_EQ(query->getSort(), BSONObj());
 
         checkReadConcern(request.cmdObj, Timestamp(0, 0), repl::OpTime::kUninitializedTerm);
@@ -1063,7 +1063,7 @@ TEST_F(ShardingCatalogClientTest, GetDatabasesForShardInvalidDoc) {
     auto future = launchAsync([this] {
         vector<string> dbs;
         const auto status =
-            catalogClient()->getDatabasesForShard(operationContext(), "shard0000", &dbs);
+            catalogClient()->getDatabasesForShard(operationContext(), ShardId("shard0000"), &dbs);
 
         ASSERT_EQ(ErrorCodes::TypeMismatch, status);
         ASSERT_EQ(0U, dbs.size());
@@ -1072,7 +1072,7 @@ TEST_F(ShardingCatalogClientTest, GetDatabasesForShardInvalidDoc) {
     onFindCommand([](const RemoteCommandRequest& request) {
         DatabaseType dbt1;
         dbt1.setName("db1");
-        dbt1.setPrimary("shard0000");
+        dbt1.setPrimary(ShardId("shard0000"));
 
         return vector<BSONObj>{
             dbt1.toBSON(),
@@ -1187,7 +1187,7 @@ TEST_F(ShardingCatalogClientTest, GetTagForChunkOneTagFound) {
     chunk.setMin(BSON("a" << 1));
     chunk.setMax(BSON("a" << 100));
     chunk.setVersion({1, 2, OID::gen()});
-    chunk.setShard("shard0000");
+    chunk.setShard(ShardId("shard0000"));
     ASSERT_OK(chunk.validate());
 
     auto future = launchAsync([this, chunk] {
@@ -1232,7 +1232,7 @@ TEST_F(ShardingCatalogClientTest, GetTagForChunkNoTagFound) {
     chunk.setMin(BSON("a" << 1));
     chunk.setMax(BSON("a" << 100));
     chunk.setVersion({1, 2, OID::gen()});
-    chunk.setShard("shard0000");
+    chunk.setShard(ShardId("shard0000"));
     ASSERT_OK(chunk.validate());
 
     auto future = launchAsync([this, chunk] {
@@ -1271,7 +1271,7 @@ TEST_F(ShardingCatalogClientTest, GetTagForChunkInvalidTagDoc) {
     chunk.setMin(BSON("a" << 1));
     chunk.setMax(BSON("a" << 100));
     chunk.setVersion({1, 2, OID::gen()});
-    chunk.setShard("shard0000");
+    chunk.setShard(ShardId("shard0000"));
     ASSERT_OK(chunk.validate());
 
     auto future = launchAsync([this, chunk] {
@@ -1311,7 +1311,7 @@ TEST_F(ShardingCatalogClientTest, UpdateDatabase) {
 
     DatabaseType dbt;
     dbt.setName("test");
-    dbt.setPrimary("shard0000");
+    dbt.setPrimary(ShardId("shard0000"));
     dbt.setSharded(true);
 
     auto future = launchAsync([this, dbt] {
@@ -1354,7 +1354,7 @@ TEST_F(ShardingCatalogClientTest, UpdateDatabaseExceededTimeLimit) {
 
     DatabaseType dbt;
     dbt.setName("test");
-    dbt.setPrimary("shard0001");
+    dbt.setPrimary(ShardId("shard0001"));
     dbt.setSharded(false);
 
     auto future = launchAsync([this, dbt] {
@@ -1450,7 +1450,7 @@ TEST_F(ShardingCatalogClientTest, ApplyChunkOpsDeprecatedSuccessfulWithCheck) {
         chunk.setMin(BSON("a" << 1));
         chunk.setMax(BSON("a" << 100));
         chunk.setVersion({1, 2, oid});
-        chunk.setShard("shard0000");
+        chunk.setShard(ShardId("shard0000"));
         return vector<BSONObj>{chunk.toBSON()};
     });
 
@@ -1621,7 +1621,8 @@ TEST_F(ShardingCatalogClientTest, createDatabaseSuccess) {
 
         DatabaseType expectedDb;
         expectedDb.setName(dbname);
-        expectedDb.setPrimary(s1.getName());  // This is the one we reported with the smallest size
+        expectedDb.setPrimary(
+            ShardId(s1.getName()));  // This is the one we reported with the smallest size
         expectedDb.setSharded(false);
 
         ASSERT_EQUALS(expectedDb.toBSON(), insert);
@@ -1910,7 +1911,8 @@ TEST_F(ShardingCatalogClientTest, createDatabaseDuplicateKeyOnInsert) {
 
         DatabaseType expectedDb;
         expectedDb.setName(dbname);
-        expectedDb.setPrimary(s1.getName());  // This is the one we reported with the smallest size
+        expectedDb.setPrimary(
+            ShardId(s1.getName()));  // This is the one we reported with the smallest size
         expectedDb.setSharded(false);
 
         ASSERT_EQUALS(expectedDb.toBSON(), insert);
@@ -1937,7 +1939,7 @@ TEST_F(ShardingCatalogClientTest, EnableShardingNoDBExists) {
     setupShards(vector<ShardType>{shard});
 
     auto shardTargeter = RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), "shard0")->getTargeter());
+        shardRegistry()->getShard(operationContext(), ShardId("shard0"))->getTargeter());
     shardTargeter->setFindHostReturnValue(HostAndPort("shard0:12"));
 
     distLock()->expectLock(
@@ -2327,7 +2329,7 @@ TEST_F(ShardingCatalogClientTest, ReadAfterOpTimeFindThenCmd) {
 
             DatabaseType dbType;
             dbType.setName("TestDB");
-            dbType.setPrimary("TestShard");
+            dbType.setPrimary(ShardId("TestShard"));
             dbType.setSharded("true");
 
             return std::make_tuple(vector<BSONObj>{dbType.toBSON()}, builder.obj());
@@ -2407,7 +2409,7 @@ TEST_F(ShardingCatalogClientTest, ReadAfterOpTimeCmdThenFind) {
 
         DatabaseType dbType;
         dbType.setName("TestDB");
-        dbType.setPrimary("TestShard");
+        dbType.setPrimary(ShardId("TestShard"));
         dbType.setSharded("true");
 
         return vector<BSONObj>{dbType.toBSON()};
@@ -2495,7 +2497,7 @@ TEST_F(ShardingCatalogClientTest, RetryOnFindCommandNetworkErrorSucceedsAtMaxRet
     onFindCommand([](const RemoteCommandRequest& request) {
         DatabaseType dbType;
         dbType.setName("TestDB");
-        dbType.setPrimary("TestShard");
+        dbType.setPrimary(ShardId("TestShard"));
         dbType.setSharded("true");
 
         return vector<BSONObj>{dbType.toBSON()};
diff --git a/src/mongo/s/catalog/sharding_catalog_client.h b/src/mongo/s/catalog/sharding_catalog_client.h
index 8317debf6db..004482b938a 100644
--- a/src/mongo/s/catalog/sharding_catalog_client.h
+++ b/src/mongo/s/catalog/sharding_catalog_client.h
@@ -148,7 +148,7 @@ public:
      * the current draining status. See ShardDrainingStatus enum definition for more details.
      */
     virtual StatusWith<ShardDrainingStatus> removeShard(OperationContext* txn,
-                                                        const std::string& name) = 0;
+                                                        const ShardId& name) = 0;
 
     /**
      * Updates or creates the metadata for a given database.
@@ -222,7 +222,7 @@ public:
      * Returns a !OK status if an error occurs.
      */
     virtual Status getDatabasesForShard(OperationContext* txn,
-                                        const std::string& shardName,
+                                        const ShardId& shardId,
                                         std::vector<std::string>* dbs) = 0;
 
     /**
diff --git a/src/mongo/s/catalog/sharding_catalog_client_mock.cpp b/src/mongo/s/catalog/sharding_catalog_client_mock.cpp
index e13711c040c..2095ceef887 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_mock.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_client_mock.cpp
@@ -68,7 +68,7 @@ Status ShardingCatalogClientMock::shardCollection(OperationContext* txn,
 }
 
 StatusWith<ShardDrainingStatus> ShardingCatalogClientMock::removeShard(OperationContext* txn,
-                                                                       const string& name) {
+                                                                       const ShardId& name) {
     return ShardDrainingStatus::COMPLETED;
 }
 
@@ -106,7 +106,7 @@ Status ShardingCatalogClientMock::dropCollection(OperationContext* txn, const Na
 }
 
 Status ShardingCatalogClientMock::getDatabasesForShard(OperationContext* txn,
-                                                       const string& shardName,
+                                                       const ShardId& shardName,
                                                        vector<string>* dbs) {
     return {ErrorCodes::InternalError, "Method not implemented"};
 }
diff --git a/src/mongo/s/catalog/sharding_catalog_client_mock.h b/src/mongo/s/catalog/sharding_catalog_client_mock.h
index 1bd8c5841e3..9edcf9b1391 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_mock.h
+++ b/src/mongo/s/catalog/sharding_catalog_client_mock.h
@@ -55,7 +55,7 @@ public:
                            const std::set<ShardId>& initShardIds) override;
 
     StatusWith<ShardDrainingStatus> removeShard(OperationContext* txn,
-                                                const std::string& name) override;
+                                                const ShardId& name) override;
 
     Status updateDatabase(OperationContext* txn,
                           const std::string& dbName,
@@ -79,7 +79,7 @@ public:
     Status dropCollection(OperationContext* txn, const NamespaceString& ns) override;
 
     Status getDatabasesForShard(OperationContext* txn,
-                                const std::string& shardName,
+                                const ShardId& shardName,
                                 std::vector<std::string>* dbs) override;
 
     Status getChunks(OperationContext* txn,
diff --git a/src/mongo/s/catalog/type_chunk.cpp b/src/mongo/s/catalog/type_chunk.cpp
index 1ab80f0e674..111aa67a625 100644
--- a/src/mongo/s/catalog/type_chunk.cpp
+++ b/src/mongo/s/catalog/type_chunk.cpp
@@ -195,7 +195,7 @@ Status ChunkType::validate() const {
         return Status(ErrorCodes::NoSuchKey, str::stream() << "missing version field");
     }
 
-    if (!_shard.is_initialized() || _shard->empty()) {
+    if (!_shard.is_initialized() || !_shard->isValid()) {
         return Status(ErrorCodes::NoSuchKey,
                       str::stream() << "missing " << shard.name() << " field");
     }
@@ -237,7 +237,7 @@ BSONObj ChunkType::toBSON() const {
     if (_max)
         builder.append(max.name(), getMax());
     if (_shard)
-        builder.append(shard.name(), getShard());
+        builder.append(shard.name(), getShard().toString());
     if (_version)
         _version->appendForChunk(&builder);
     if (_jumbo)
@@ -276,8 +276,8 @@ void ChunkType::setVersion(const ChunkVersion& version) {
     _version = version;
 }
 
-void ChunkType::setShard(const std::string& shard) {
-    invariant(!shard.empty());
+void ChunkType::setShard(const ShardId& shard) {
+    invariant(shard.isValid());
     _shard = shard;
 }
 
diff --git a/src/mongo/s/catalog/type_chunk.h b/src/mongo/s/catalog/type_chunk.h
index f988a09028d..a7a0e1f7e30 100644
--- a/src/mongo/s/catalog/type_chunk.h
+++ b/src/mongo/s/catalog/type_chunk.h
@@ -33,6 +33,7 @@
 
 #include "mongo/bson/bsonobj.h"
 #include "mongo/s/chunk_version.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 
@@ -158,10 +159,10 @@ public:
     }
     void setVersion(const ChunkVersion& version);
 
-    const std::string& getShard() const {
+    const ShardId& getShard() const {
         return _shard.get();
     }
-    void setShard(const std::string& shard);
+    void setShard(const ShardId& shard);
 
     bool getJumbo() const {
         return _jumbo.get_value_or(false);
@@ -180,7 +181,7 @@ private:
     // (M)  version of this chunk
     boost::optional<ChunkVersion> _version;
     // (M)  shard this chunk lives in
-    boost::optional<std::string> _shard;
+    boost::optional<ShardId> _shard;
     // (O)  too big to move?
     boost::optional<bool> _jumbo;
 };
diff --git a/src/mongo/s/catalog/type_database.cpp b/src/mongo/s/catalog/type_database.cpp
index 24de84c838c..9ccf117ea87 100644
--- a/src/mongo/s/catalog/type_database.cpp
+++ b/src/mongo/s/catalog/type_database.cpp
@@ -86,7 +86,7 @@ Status DatabaseType::validate() const {
         return Status(ErrorCodes::NoSuchKey, "missing name");
     }
 
-    if (!_primary.is_initialized() || _primary->empty()) {
+    if (!_primary.is_initialized() || !_primary->isValid()) {
         return Status(ErrorCodes::NoSuchKey, "missing primary");
     }
 
@@ -100,7 +100,7 @@ Status DatabaseType::validate() const {
 BSONObj DatabaseType::toBSON() const {
     BSONObjBuilder builder;
     builder.append(name.name(), _name.get_value_or(""));
-    builder.append(primary.name(), _primary.get_value_or(""));
+    builder.append(primary.name(), _primary.get_value_or(ShardId()).toString());
     builder.append(sharded.name(), _sharded.get_value_or(false));
 
     return builder.obj();
@@ -115,8 +115,8 @@ void DatabaseType::setName(const std::string& name) {
     _name = name;
 }
 
-void DatabaseType::setPrimary(const std::string& primary) {
-    invariant(!primary.empty());
+void DatabaseType::setPrimary(const ShardId& primary) {
+    invariant(primary.isValid());
     _primary = primary;
 }
 
diff --git a/src/mongo/s/catalog/type_database.h b/src/mongo/s/catalog/type_database.h
index e452bd826a2..c1948f1132c 100644
--- a/src/mongo/s/catalog/type_database.h
+++ b/src/mongo/s/catalog/type_database.h
@@ -32,6 +32,7 @@
 #include <string>
 
 #include "mongo/db/jsobj.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 
@@ -82,10 +83,10 @@ public:
     }
     void setName(const std::string& name);
 
-    const std::string& getPrimary() const {
+    const ShardId& getPrimary() const {
         return _primary.get();
     }
-    void setPrimary(const std::string& primary);
+    void setPrimary(const ShardId& primary);
 
     bool getSharded() const {
         return _sharded.get();
@@ -100,7 +101,7 @@ private:
 
     // Required primary shard (must be set even if the database is sharded, because there
     // might be collections, which are unsharded).
-    boost::optional<std::string> _primary;
+    boost::optional<ShardId> _primary;
 
     // Required whether sharding is enabled for this database. Even though this field is of
     // type optional, it is only used as an indicator that the value was explicitly set.
diff --git a/src/mongo/s/chunk_diff.h b/src/mongo/s/chunk_diff.h
index 384f95e7df9..578ca7e51e9 100644
--- a/src/mongo/s/chunk_diff.h
+++ b/src/mongo/s/chunk_diff.h
@@ -128,7 +128,7 @@ protected:
     virtual std::pair<BSONObj, ValType> rangeFor(OperationContext* txn,
                                                  const ChunkType& chunk) const = 0;
 
-    virtual ShardId shardFor(OperationContext* txn, const std::string& name) const = 0;
+    virtual ShardId shardFor(OperationContext* txn, const ShardId& name) const = 0;
 
 private:
     void _assertAttached() const;
diff --git a/src/mongo/s/chunk_diff_test.cpp b/src/mongo/s/chunk_diff_test.cpp
index 46cbce4dabc..51dd7ea1617 100644
--- a/src/mongo/s/chunk_diff_test.cpp
+++ b/src/mongo/s/chunk_diff_test.cpp
@@ -68,7 +68,7 @@ public:
         return make_pair(chunk.getMin(), chunk.getMax());
     }
 
-    virtual ShardId shardFor(OperationContext* txn, const string& name) const {
+    virtual ShardId shardFor(OperationContext* txn, const ShardId& name) const {
         return name;
     }
 };
@@ -105,7 +105,7 @@ void convertBSONArrayToChunkTypes(const vector<BSONObj>& chunksArray,
 class ChunkDiffUnitTest : public mongo::unittest::Test {
 protected:
     typedef map<BSONObj, BSONObj, BSONObjCmp> RangeMap;
-    typedef map<string, ChunkVersion> VersionMap;
+    typedef map<ShardId, ChunkVersion> VersionMap;
 
     ChunkDiffUnitTest() = default;
     ~ChunkDiffUnitTest() = default;
diff --git a/src/mongo/s/chunk_manager.cpp b/src/mongo/s/chunk_manager.cpp
index 0dcad211c7e..031721d6324 100644
--- a/src/mongo/s/chunk_manager.cpp
+++ b/src/mongo/s/chunk_manager.cpp
@@ -97,8 +97,8 @@ public:
         return make_pair(chunk.getMax(), c);
     }
 
-    string shardFor(OperationContext* txn, const string& hostName) const final {
-        const auto shard = grid.shardRegistry()->getShard(txn, hostName);
+    ShardId shardFor(OperationContext* txn, const ShardId& shardId) const final {
+        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
         return shard->getId();
     }
 
@@ -674,13 +674,13 @@ IndexBounds ChunkManager::collapseQuerySolution(const QuerySolutionNode* node) {
     return bounds;
 }
 
-bool ChunkManager::compatibleWith(const ChunkManager& other, const string& shardName) const {
+bool ChunkManager::compatibleWith(const ChunkManager& other, const ShardId& shardName) const {
     // Return true if the shard version is the same in the two chunk managers
     // TODO: This doesn't need to be so strong, just major vs
     return other.getVersion(shardName).equals(getVersion(shardName));
 }
 
-ChunkVersion ChunkManager::getVersion(const std::string& shardName) const {
+ChunkVersion ChunkManager::getVersion(const ShardId& shardName) const {
     ShardVersionMap::const_iterator i = _shardVersions.find(shardName);
     if (i == _shardVersions.end()) {
         // Shards without explicitly tracked shard versions (meaning they have
diff --git a/src/mongo/s/chunk_manager.h b/src/mongo/s/chunk_manager.h
index 49009d8abb6..e2178feddaf 100644
--- a/src/mongo/s/chunk_manager.h
+++ b/src/mongo/s/chunk_manager.h
@@ -57,7 +57,7 @@ typedef std::map<BSONObj, std::shared_ptr<Chunk>, BSONObjCmp> ChunkMap;
 
 class ChunkManager {
 public:
-    typedef std::map<std::string, ChunkVersion> ShardVersionMap;
+    typedef std::map<ShardId, ChunkVersion> ShardVersionMap;
 
     // Loads a new chunk manager from a collection document
     explicit ChunkManager(const CollectionType& coll);
@@ -164,11 +164,11 @@ public:
     /**
      * Returns true if, for this shard, the chunks are identical in both chunk managers
      */
-    bool compatibleWith(const ChunkManager& other, const std::string& shard) const;
+    bool compatibleWith(const ChunkManager& other, const ShardId& shard) const;
 
     std::string toString() const;
 
-    ChunkVersion getVersion(const std::string& shardName) const;
+    ChunkVersion getVersion(const ShardId& shardName) const;
     ChunkVersion getVersion() const;
 
     void _printChunks() const;
diff --git a/src/mongo/s/chunk_manager_targeter.cpp b/src/mongo/s/chunk_manager_targeter.cpp
index c9e9bcb76de..6f1578ef5f1 100644
--- a/src/mongo/s/chunk_manager_targeter.cpp
+++ b/src/mongo/s/chunk_manager_targeter.cpp
@@ -188,21 +188,22 @@ ChunkVersion getShardVersion(StringData shardName,
  */
 CompareResult compareAllShardVersions(const ChunkManager* cachedChunkManager,
                                       const Shard* cachedPrimary,
-                                      const map<string, ChunkVersion>& remoteShardVersions) {
+                                      const map<ShardId, ChunkVersion>& remoteShardVersions) {
     CompareResult finalResult = CompareResult_GTE;
 
-    for (map<string, ChunkVersion>::const_iterator it = remoteShardVersions.begin();
+    for (map<ShardId, ChunkVersion>::const_iterator it = remoteShardVersions.begin();
          it != remoteShardVersions.end();
          ++it) {
         // Get the remote and cached version for the next shard
-        const string& shardName = it->first;
+        const ShardId& shardName = it->first;
         const ChunkVersion& remoteShardVersion = it->second;
 
         ChunkVersion cachedShardVersion;
 
         try {
             // Throws b/c shard constructor throws
-            cachedShardVersion = getShardVersion(shardName, cachedChunkManager, cachedPrimary);
+            cachedShardVersion =
+                getShardVersion(shardName.toString(), cachedChunkManager, cachedPrimary);
         } catch (const DBException& ex) {
             warning() << "could not lookup shard " << shardName
                       << " in local cache, shard metadata may have changed"
@@ -576,7 +577,8 @@ void ChunkManagerTargeter::noteStaleResponse(const ShardEndpoint& endpoint,
     if (staleInfo["vWanted"].eoo()) {
         // If we don't have a vWanted sent, assume the version is higher than our current
         // version.
-        remoteShardVersion = getShardVersion(endpoint.shardName, _manager.get(), _primary.get());
+        remoteShardVersion =
+            getShardVersion(endpoint.shardName.toString(), _manager.get(), _primary.get());
         remoteShardVersion.incMajor();
     } else {
         remoteShardVersion = ChunkVersion::fromBSON(staleInfo, "vWanted");
@@ -584,7 +586,7 @@ void ChunkManagerTargeter::noteStaleResponse(const ShardEndpoint& endpoint,
 
     ShardVersionMap::iterator it = _remoteShardVersions.find(endpoint.shardName);
     if (it == _remoteShardVersions.end()) {
-        _remoteShardVersions.insert(make_pair(endpoint.shardName, remoteShardVersion));
+        _remoteShardVersions.insert(std::make_pair(endpoint.shardName, remoteShardVersion));
     } else {
         ChunkVersion& previouslyNotedVersion = it->second;
         if (previouslyNotedVersion.hasEqualEpoch(remoteShardVersion)) {
diff --git a/src/mongo/s/chunk_manager_targeter.h b/src/mongo/s/chunk_manager_targeter.h
index b9fa547d89e..06c823bbcf1 100644
--- a/src/mongo/s/chunk_manager_targeter.h
+++ b/src/mongo/s/chunk_manager_targeter.h
@@ -110,7 +110,7 @@ private:
         RefreshType_ReloadDatabase
     };
 
-    typedef std::map<std::string, ChunkVersion> ShardVersionMap;
+    typedef std::map<ShardId, ChunkVersion> ShardVersionMap;
 
 
     /**
diff --git a/src/mongo/s/chunk_manager_tests.cpp b/src/mongo/s/chunk_manager_tests.cpp
index d674e94bc51..08ac87e954c 100644
--- a/src/mongo/s/chunk_manager_tests.cpp
+++ b/src/mongo/s/chunk_manager_tests.cpp
@@ -138,7 +138,7 @@ protected:
             ASSERT(version.epoch() == epoch);
 
             // Check chunk's shard id.
-            ASSERT(chunk[ChunkType::shard()].String() == _shardId);
+            ASSERT(chunk[ChunkType::shard()].String() == _shardId.toString());
 
             return RemoteCommandResponse(BSON("ok" << 1), BSONObj(), Milliseconds(1));
         });
diff --git a/src/mongo/s/client/SConscript b/src/mongo/s/client/SConscript
index dbc890279c2..6c1263d354d 100644
--- a/src/mongo/s/client/SConscript
+++ b/src/mongo/s/client/SConscript
@@ -79,6 +79,7 @@ env.Library(
     ],
     LIBDEPS=[
         '$BUILD_DIR/mongo/base',
+        '$BUILD_DIR/mongo/s/shard_id',
     ]
 )
 
diff --git a/src/mongo/s/client/shard.h b/src/mongo/s/client/shard.h
index 145bf1e2593..cf57f4ef1ac 100644
--- a/src/mongo/s/client/shard.h
+++ b/src/mongo/s/client/shard.h
@@ -33,14 +33,13 @@
 #include "mongo/client/read_preference.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/repl/optime.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 
 class OperationContext;
 class RemoteCommandTargeter;
 
-using ShardId = std::string;
-
 /**
  * Presents an interface for talking to shards, regardless of whether that shard is remote or is
  * the current (local) shard.
diff --git a/src/mongo/s/client/shard_local.cpp b/src/mongo/s/client/shard_local.cpp
index 26f17aaa029..58db95ad74c 100644
--- a/src/mongo/s/client/shard_local.cpp
+++ b/src/mongo/s/client/shard_local.cpp
@@ -78,7 +78,7 @@ void ShardLocal::updateReplSetMonitor(const HostAndPort& remoteHost,
 }
 
 std::string ShardLocal::toString() const {
-    return getId() + ":<local>";
+    return getId().toString() + ":<local>";
 }
 
 bool ShardLocal::isRetriableError(ErrorCodes::Error code, RetryPolicy options) {
diff --git a/src/mongo/s/client/shard_local_test.cpp b/src/mongo/s/client/shard_local_test.cpp
index 45faebc4a9e..b04ab897ead 100644
--- a/src/mongo/s/client/shard_local_test.cpp
+++ b/src/mongo/s/client/shard_local_test.cpp
@@ -76,7 +76,7 @@ void ShardLocalTest::setUp() {
     ServiceContextMongoDTest::setUp();
     Client::initThreadIfNotAlready();
     _txn = getGlobalServiceContext()->makeOperationContext(&cc());
-    _shardLocal = stdx::make_unique<ShardLocal>("shardOrConfig");
+    _shardLocal = stdx::make_unique<ShardLocal>(ShardId("shardOrConfig"));
     const repl::ReplSettings replSettings = {};
     repl::setGlobalReplicationCoordinator(new repl::ReplicationCoordinatorMock(replSettings));
 }
diff --git a/src/mongo/s/client/shard_registry.cpp b/src/mongo/s/client/shard_registry.cpp
index 34307cd1fe2..13135db1142 100644
--- a/src/mongo/s/client/shard_registry.cpp
+++ b/src/mongo/s/client/shard_registry.cpp
@@ -119,7 +119,7 @@ shared_ptr<Shard> ShardRegistry::getConfigShard() const {
 }
 
 unique_ptr<Shard> ShardRegistry::createConnection(const ConnectionString& connStr) const {
-    return _shardFactory->createUniqueShard("<unnamed>", connStr);
+    return _shardFactory->createUniqueShard(ShardId("<unnamed>"), connStr);
 }
 
 shared_ptr<Shard> ShardRegistry::lookupRSName(const string& name) const {
@@ -127,7 +127,7 @@ shared_ptr<Shard> ShardRegistry::lookupRSName(const string& name) const {
 }
 
 void ShardRegistry::getAllShardIds(vector<ShardId>* all) const {
-    std::set<string> seen;
+    std::set<ShardId> seen;
     _data.getAllShardIds(seen);
     all->assign(seen.begin(), seen.end());
 }
@@ -146,7 +146,7 @@ void ShardRegistry::updateReplSetHosts(const ConnectionString& newConnString) {
 void ShardRegistry::startup() {
     stdx::unique_lock<stdx::mutex> reloadLock(_reloadMutex);
     invariant(_initConfigServerCS.isValid());
-    auto configShard = _shardFactory->createShard("config", _initConfigServerCS);
+    auto configShard = _shardFactory->createShard(ShardId("config"), _initConfigServerCS);
     _data.addConfigShard(configShard);
     // set to invalid so it cant be started more than once.
     _initConfigServerCS = ConnectionString();
@@ -302,11 +302,11 @@ void ShardRegistryData::toBSON(BSONObjBuilder* result) const {
     }
 }
 
-void ShardRegistryData::getAllShardIds(std::set<string>& seen) const {
+void ShardRegistryData::getAllShardIds(std::set<ShardId>& seen) const {
     stdx::lock_guard<stdx::mutex> lk(_mutex);
     for (auto i = _lookup.begin(); i != _lookup.end(); ++i) {
         const auto& s = i->second;
-        if (s->getId() == "config") {
+        if (s->getId().toString() == "config") {
             continue;
         }
         seen.insert(s->getId());
@@ -377,8 +377,8 @@ void ShardRegistryData::_addShard_inlock(const std::shared_ptr<Shard>& shard) {
         // CUSTOM connection strings (ie "$dummy:10000) become DBDirectClient connections which
         // always return "localhost" as their response to getServerAddress().  This is just for
         // making dbtest work.
-        _lookup["localhost"] = shard;
-        _hostLookup[HostAndPort{"localhost"}] = shard;
+        _lookup[ShardId("localhost")] = shard;
+        _hostLookup[HostAndPort("localhost")] = shard;
     }
 
     // TODO: The only reason to have the shard host names in the lookup table is for the
diff --git a/src/mongo/s/client/shard_registry.h b/src/mongo/s/client/shard_registry.h
index e65987485e9..e384a53feea 100644
--- a/src/mongo/s/client/shard_registry.h
+++ b/src/mongo/s/client/shard_registry.h
@@ -115,7 +115,7 @@ private:
 
     // Protects the lookup maps below.
     mutable stdx::mutex _mutex;
-    using ShardMap = std::unordered_map<ShardId, std::shared_ptr<Shard>>;
+    using ShardMap = std::unordered_map<ShardId, std::shared_ptr<Shard>, ShardId::Hasher>;
 
     // Map of both shardName -> Shard and hostName -> Shard
     ShardMap _lookup;
diff --git a/src/mongo/s/client/shard_registry_data_test.cpp b/src/mongo/s/client/shard_registry_data_test.cpp
index 162ebb52c78..a005cb1aae8 100644
--- a/src/mongo/s/client/shard_registry_data_test.cpp
+++ b/src/mongo/s/client/shard_registry_data_test.cpp
@@ -85,7 +85,7 @@ private:
 
 TEST_F(ShardRegistryDataTest, AddConfigShard) {
     ConnectionString configCS("rs/dummy1:1234,dummy2:2345,dummy3:3456", ConnectionString::SET);
-    auto configShard = shardFactory()->createShard("config", configCS);
+    auto configShard = shardFactory()->createShard(ShardId("config"), configCS);
 
     ShardRegistryData data;
     data.addConfigShard(configShard);
diff --git a/src/mongo/s/client/shard_remote.cpp b/src/mongo/s/client/shard_remote.cpp
index 1ed6abe2d41..3aa44218b4f 100644
--- a/src/mongo/s/client/shard_remote.cpp
+++ b/src/mongo/s/client/shard_remote.cpp
@@ -177,7 +177,7 @@ void ShardRemote::updateReplSetMonitor(const HostAndPort& remoteHost,
 }
 
 std::string ShardRemote::toString() const {
-    return getId() + ":" + _originalConnString.toString();
+    return getId().toString() + ":" + _originalConnString.toString();
 }
 
 const BSONObj& ShardRemote::_getMetadataForCommand(const ReadPreferenceSetting& readPref) {
diff --git a/src/mongo/s/commands/cluster_count_cmd.cpp b/src/mongo/s/commands/cluster_count_cmd.cpp
index 4bb96e6b086..2a4ca984a16 100644
--- a/src/mongo/s/commands/cluster_count_cmd.cpp
+++ b/src/mongo/s/commands/cluster_count_cmd.cpp
@@ -162,16 +162,16 @@ public:
         for (vector<Strategy::CommandResult>::const_iterator iter = countResult.begin();
              iter != countResult.end();
              ++iter) {
-            const string& shardName = iter->shardTargetId;
+            const ShardId& shardName = iter->shardTargetId;
 
             if (iter->result["ok"].trueValue()) {
                 long long shardCount = iter->result["n"].numberLong();
 
-                shardSubTotal.appendNumber(shardName, shardCount);
+                shardSubTotal.appendNumber(shardName.toString(), shardCount);
                 total += shardCount;
             } else {
                 shardSubTotal.doneFast();
-                errmsg = "failed on : " + shardName;
+                errmsg = "failed on : " + shardName.toString();
                 result.append("cause", iter->result);
 
                 // Add "code" to the top-level response, if the failure of the sharded command
diff --git a/src/mongo/s/commands/cluster_explain.cpp b/src/mongo/s/commands/cluster_explain.cpp
index e38a2d072b5..fa4b231741a 100644
--- a/src/mongo/s/commands/cluster_explain.cpp
+++ b/src/mongo/s/commands/cluster_explain.cpp
@@ -218,7 +218,7 @@ void ClusterExplain::buildPlannerInfo(OperationContext* txn,
         BSONObj queryPlanner = shardResults[i].result["queryPlanner"].Obj();
         BSONObj serverInfo = shardResults[i].result["serverInfo"].Obj();
 
-        singleShardBob.append("shardName", shardResults[i].shardTargetId);
+        singleShardBob.append("shardName", shardResults[i].shardTargetId.toString());
         {
             const auto shard = grid.shardRegistry()->getShard(txn, shardResults[i].shardTargetId);
             singleShardBob.append("connectionString", shard->getConnString().toString());
@@ -291,7 +291,7 @@ void ClusterExplain::buildExecStats(const vector<Strategy::CommandResult>& shard
         BSONObj execStats = shardResults[i].result["executionStats"].Obj();
         BSONObj execStages = execStats["executionStages"].Obj();
 
-        singleShardBob.append("shardName", shardResults[i].shardTargetId);
+        singleShardBob.append("shardName", shardResults[i].shardTargetId.toString());
 
         // Append error-related fields, if present.
         if (!execStats["executionSuccess"].eoo()) {
@@ -323,7 +323,7 @@ void ClusterExplain::buildExecStats(const vector<Strategy::CommandResult>& shard
     for (size_t i = 0; i < shardResults.size(); i++) {
         BSONObjBuilder singleShardBob(execShardsBuilder.subobjStart());
 
-        singleShardBob.append("shardName", shardResults[i].shardTargetId);
+        singleShardBob.append("shardName", shardResults[i].shardTargetId.toString());
 
         BSONObj execStats = shardResults[i].result["executionStats"].Obj();
         vector<BSONElement> allPlans = execStats["allPlansExecution"].Array();
diff --git a/src/mongo/s/commands/cluster_fsync_cmd.cpp b/src/mongo/s/commands/cluster_fsync_cmd.cpp
index b3dc4e5edcd..8a1ce646c2e 100644
--- a/src/mongo/s/commands/cluster_fsync_cmd.cpp
+++ b/src/mongo/s/commands/cluster_fsync_cmd.cpp
@@ -101,7 +101,7 @@ public:
             uassertStatusOK(response.commandStatus);
             BSONObj x = std::move(response.response);
 
-            sub.append(s->getId(), x);
+            sub.append(s->getId().toString(), x);
 
             if (!x["ok"].trueValue()) {
                 ok = false;
diff --git a/src/mongo/s/commands/cluster_index_filter_cmd.cpp b/src/mongo/s/commands/cluster_index_filter_cmd.cpp
index 14e8562024c..a1f4d40d81d 100644
--- a/src/mongo/s/commands/cluster_index_filter_cmd.cpp
+++ b/src/mongo/s/commands/cluster_index_filter_cmd.cpp
@@ -126,7 +126,7 @@ public:
 
             // Append shard result as a sub object.
             // Name the field after the shard.
-            result.append(cmdResult.shardTargetId, cmdResult.result);
+            result.append(cmdResult.shardTargetId.toString(), cmdResult.result);
         }
 
         return clusterCmdResult;
diff --git a/src/mongo/s/commands/cluster_list_databases_cmd.cpp b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
index b9fcc41af54..3b911f97588 100644
--- a/src/mongo/s/commands/cluster_list_databases_cmd.cpp
+++ b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
@@ -130,7 +130,7 @@ public:
                     bb.reset(new BSONObjBuilder());
                 }
 
-                bb->appendNumber(s->getId(), size);
+                bb->appendNumber(s->getId().toString(), size);
             }
         }
 
diff --git a/src/mongo/s/commands/cluster_plan_cache_cmd.cpp b/src/mongo/s/commands/cluster_plan_cache_cmd.cpp
index 9da09c470a0..1973c93d7d3 100644
--- a/src/mongo/s/commands/cluster_plan_cache_cmd.cpp
+++ b/src/mongo/s/commands/cluster_plan_cache_cmd.cpp
@@ -141,7 +141,7 @@ bool ClusterPlanCacheCmd::run(OperationContext* txn,
 
         // Append shard result as a sub object.
         // Name the field after the shard.
-        string shardName = cmdResult.shardTargetId;
+        string shardName = cmdResult.shardTargetId.toString();
         result.append(shardName, cmdResult.result);
     }
 
diff --git a/src/mongo/s/commands/cluster_remove_shard_cmd.cpp b/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
index a82bba5e38e..0a8c4ff318f 100644
--- a/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
+++ b/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
@@ -87,7 +87,7 @@ public:
                      BSONObjBuilder& result) {
         const string target = cmdObj.firstElement().valuestrsafe();
 
-        const auto s = grid.shardRegistry()->getShard(txn, target);
+        const auto s = grid.shardRegistry()->getShard(txn, ShardId(target));
         if (!s) {
             string msg(str::stream() << "Could not drop shard '" << target
                                      << "' because it does not exist");
@@ -131,17 +131,18 @@ public:
             case ShardDrainingStatus::STARTED:
                 result.append("msg", "draining started successfully");
                 result.append("state", "started");
-                result.append("shard", s->getId());
+                result.append("shard", s->getId().toString());
                 result.appendElements(dbInfo);
                 break;
             case ShardDrainingStatus::ONGOING: {
                 vector<ChunkType> chunks;
-                Status status = catalogClient->getChunks(txn,
-                                                         BSON(ChunkType::shard(s->getId())),
-                                                         BSONObj(),
-                                                         boost::none,  // return all
-                                                         &chunks,
-                                                         nullptr);
+                Status status =
+                    catalogClient->getChunks(txn,
+                                             BSON(ChunkType::shard(s->getId().toString())),
+                                             BSONObj(),
+                                             boost::none,  // return all
+                                             &chunks,
+                                             nullptr);
                 if (!status.isOK()) {
                     return appendCommandStatus(result, status);
                 }
@@ -161,7 +162,7 @@ public:
             case ShardDrainingStatus::COMPLETED:
                 result.append("msg", "removeshard completed successfully");
                 result.append("state", "completed");
-                result.append("shard", s->getId());
+                result.append("shard", s->getId().toString());
         }
 
         return true;
diff --git a/src/mongo/s/commands/cluster_user_management_commands.cpp b/src/mongo/s/commands/cluster_user_management_commands.cpp
index fd425be5691..93e344c766c 100644
--- a/src/mongo/s/commands/cluster_user_management_commands.cpp
+++ b/src/mongo/s/commands/cluster_user_management_commands.cpp
@@ -846,7 +846,7 @@ Status runUpgradeOnAllShards(OperationContext* txn,
     // Upgrade each shard in turn, stopping on first failure.
     auto shardRegistry = grid.shardRegistry();
     shardRegistry->reload(txn);
-    vector<string> shardIds;
+    vector<ShardId> shardIds;
     shardRegistry->getAllShardIds(&shardIds);
 
     bool hasWCError = false;
diff --git a/src/mongo/s/commands/cluster_write_cmd.cpp b/src/mongo/s/commands/cluster_write_cmd.cpp
index eafdb4940a8..19a9969de6c 100644
--- a/src/mongo/s/commands/cluster_write_cmd.cpp
+++ b/src/mongo/s/commands/cluster_write_cmd.cpp
@@ -270,7 +270,7 @@ private:
             auto shard = grid.shardRegistry()->getShard(txn, endpoint->shardName);
             if (!shard) {
                 return Status(ErrorCodes::ShardNotFound,
-                              "Could not find shard with id " + endpoint->shardName);
+                              "Could not find shard with id " + endpoint->shardName.toString());
             }
             auto swHostAndPort = shard->getTargeter()->findHost(readPref);
             if (!swHostAndPort.isOK()) {
diff --git a/src/mongo/s/commands/commands_public.cpp b/src/mongo/s/commands/commands_public.cpp
index f3115964c1b..1323ea8e215 100644
--- a/src/mongo/s/commands/commands_public.cpp
+++ b/src/mongo/s/commands/commands_public.cpp
@@ -447,7 +447,7 @@ public:
         bool isValid = true;
         bool errored = false;
         for (const auto& cmdResult : results) {
-            const string& shardName = cmdResult.shardTargetId;
+            const ShardId& shardName = cmdResult.shardTargetId;
             BSONObj result = cmdResult.result;
             const BSONElement valid = result["valid"];
             if (!valid.trueValue()) {
@@ -459,7 +459,7 @@ public:
                 errmsg = result["errmsg"].toString();
                 errored = true;
             }
-            rawResBuilder.append(shardName, result);
+            rawResBuilder.append(shardName.toString(), result);
         }
         rawResBuilder.done();
 
@@ -701,7 +701,7 @@ public:
         auto conf = uassertStatusOK(grid.catalogCache()->getDatabase(txn, dbName));
         if (!conf->isShardingEnabled() || !conf->isSharded(fullns)) {
             result.appendBool("sharded", false);
-            result.append("primary", conf->getPrimaryId());
+            result.append("primary", conf->getPrimaryId().toString());
 
             return passthrough(txn, conf.get(), cmdObj, result);
         }
@@ -811,7 +811,7 @@ public:
                     warning() << "mongos collstats doesn't know about: " << e.fieldName();
                 }
             }
-            shardStats.append(shardId, res);
+            shardStats.append(shardId.toString(), res);
         }
 
         result.append("ns", fullns);
@@ -1288,7 +1288,7 @@ public:
                 } catch (DBException& e) {
                     // This is handled below and logged
                     Strategy::CommandResult errResult;
-                    errResult.shardTargetId = "";
+                    errResult.shardTargetId = ShardId();
                     errResult.result = BSON("errmsg" << e.what() << "ok" << 0);
                     results.push_back(errResult);
                 }
@@ -1400,7 +1400,7 @@ public:
 
             futures.push_back(
                 Future::spawnCommand(shard->getConnString().toString(), dbName, cmdObj, options));
-            shardArray.append(shardId);
+            shardArray.append(shardId.toString());
         }
 
         multimap<double, BSONObj> results;  // TODO: maybe use merge-sort instead
diff --git a/src/mongo/s/commands/run_on_all_shards_cmd.cpp b/src/mongo/s/commands/run_on_all_shards_cmd.cpp
index 5e273e159ea..e83e6d353cb 100644
--- a/src/mongo/s/commands/run_on_all_shards_cmd.cpp
+++ b/src/mongo/s/commands/run_on_all_shards_cmd.cpp
@@ -119,7 +119,7 @@ bool RunOnAllShardsCommand::run(OperationContext* txn,
         if (res->join(txn)) {
             // success :)
             BSONObj result = res->result();
-            results.emplace_back(*shardIdsIt, result);
+            results.emplace_back(shardIdsIt->toString(), result);
             subobj.append(res->getServer(), result);
 
             if (!hasWCError) {
@@ -146,7 +146,7 @@ bool RunOnAllShardsCommand::run(OperationContext* txn,
             BSONElement errmsgObj = result["errmsg"];
             if (errmsgObj.eoo() || errmsgObj.String().empty()) {
                 // it was fixed!
-                results.emplace_back(*shardIdsIt, result);
+                results.emplace_back(shardIdsIt->toString(), result);
                 subobj.append(res->getServer(), result);
                 continue;
             }
@@ -168,7 +168,7 @@ bool RunOnAllShardsCommand::run(OperationContext* txn,
         } else if (commonErrCode != errCode) {
             commonErrCode = 0;
         }
-        results.emplace_back(*shardIdsIt, result);
+        results.emplace_back(shardIdsIt->toString(), result);
         subobj.append(res->getServer(), result);
     }
 
diff --git a/src/mongo/s/commands/sharded_command_processing.cpp b/src/mongo/s/commands/sharded_command_processing.cpp
index f873a4e0265..0c44761b9c2 100644
--- a/src/mongo/s/commands/sharded_command_processing.cpp
+++ b/src/mongo/s/commands/sharded_command_processing.cpp
@@ -31,10 +31,11 @@
 #include "mongo/s/commands/sharded_command_processing.h"
 
 #include "mongo/rpc/write_concern_error_detail.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 
-void appendWriteConcernErrorToCmdResponse(const std::string& shardID,
+void appendWriteConcernErrorToCmdResponse(const ShardId& shardId,
                                           const BSONElement& wcErrorElem,
                                           BSONObjBuilder& responseBuilder) {
     WriteConcernErrorDetail wcError;
@@ -44,7 +45,7 @@ void appendWriteConcernErrorToCmdResponse(const std::string& shardID,
         wcError.setErrMessage("Failed to parse writeConcernError: " + wcErrorObj.toString() +
                               ", Received error: " + errMsg);
     }
-    wcError.setErrMessage(wcError.getErrMessage() + " at " + shardID);
+    wcError.setErrMessage(wcError.getErrMessage() + " at " + shardId.toString());
     responseBuilder.append("writeConcernError", wcError.toBSON());
 }
 }  // namespace mongo
diff --git a/src/mongo/s/commands/sharded_command_processing.h b/src/mongo/s/commands/sharded_command_processing.h
index f0424424f89..18732669ef1 100644
--- a/src/mongo/s/commands/sharded_command_processing.h
+++ b/src/mongo/s/commands/sharded_command_processing.h
@@ -34,10 +34,12 @@
 
 namespace mongo {
 
+class ShardId;
+
 /**
  * This function appends the provided writeConcernError BSONElement to the sharded response.
  */
-void appendWriteConcernErrorToCmdResponse(const std::string& shardID,
+void appendWriteConcernErrorToCmdResponse(const ShardId& shardID,
                                           const BSONElement& wcErrorElem,
                                           BSONObjBuilder& responseBuilder);
 }  // namespace mongo
diff --git a/src/mongo/s/config.cpp b/src/mongo/s/config.cpp
index 5773d7a3995..723e474ca74 100644
--- a/src/mongo/s/config.cpp
+++ b/src/mongo/s/config.cpp
@@ -579,14 +579,14 @@ bool DBConfig::dropDatabase(OperationContext* txn, string& errmsg) {
         ScopedDbConnection conn(shard->getConnString(), 30.0);
         BSONObj res;
         if (!conn->dropDatabase(_name, txn->getWriteConcern(), &res)) {
-            errmsg = res.toString() + " at " + _primaryId;
+            errmsg = res.toString() + " at " + _primaryId.toString();
             return 0;
         }
         conn.done();
         if (auto wcErrorElem = res["writeConcernError"]) {
             auto wcError = wcErrorElem.Obj();
             if (auto errMsgElem = wcError["errmsg"]) {
-                errmsg = errMsgElem.str() + " at " + _primaryId;
+                errmsg = errMsgElem.str() + " at " + _primaryId.toString();
                 return false;
             }
         }
@@ -602,14 +602,14 @@ bool DBConfig::dropDatabase(OperationContext* txn, string& errmsg) {
         ScopedDbConnection conn(shard->getConnString(), 30.0);
         BSONObj res;
         if (!conn->dropDatabase(_name, txn->getWriteConcern(), &res)) {
-            errmsg = res.toString() + " at " + shardId;
+            errmsg = res.toString() + " at " + shardId.toString();
             return 0;
         }
         conn.done();
         if (auto wcErrorElem = res["writeConcernError"]) {
             auto wcError = wcErrorElem.Obj();
             if (auto errMsgElem = wcError["errmsg"]) {
-                errmsg = errMsgElem.str() + " at " + shardId;
+                errmsg = errMsgElem.str() + " at " + shardId.toString();
                 return false;
             }
         }
@@ -724,7 +724,7 @@ void ConfigServer::replicaSetChangeConfigServerUpdateHook(const string& setName,
         auto status = grid.catalogClient(txn.get())->updateConfigDocument(
             txn.get(),
             ShardType::ConfigNS,
-            BSON(ShardType::name(s->getId())),
+            BSON(ShardType::name(s->getId().toString())),
             BSON("$set" << BSON(ShardType::host(newConnectionString))),
             false);
         if (!status.isOK()) {
diff --git a/src/mongo/s/move_chunk_request.cpp b/src/mongo/s/move_chunk_request.cpp
index 8370000d511..3117f2a2cbb 100644
--- a/src/mongo/s/move_chunk_request.cpp
+++ b/src/mongo/s/move_chunk_request.cpp
@@ -86,14 +86,18 @@ StatusWith<MoveChunkRequest> MoveChunkRequest::createFromCommand(NamespaceString
     }
 
     {
-        Status status = bsonExtractStringField(obj, kFromShardId, &request._fromShardId);
+        std::string shardStr;
+        Status status = bsonExtractStringField(obj, kFromShardId, &shardStr);
+        request._fromShardId = shardStr;
         if (!status.isOK()) {
             return status;
         }
     }
 
     {
-        Status status = bsonExtractStringField(obj, kToShardId, &request._toShardId);
+        std::string shardStr;
+        Status status = bsonExtractStringField(obj, kToShardId, &shardStr);
+        request._toShardId = shardStr;
         if (!status.isOK()) {
             return status;
         }
@@ -132,8 +136,8 @@ void MoveChunkRequest::appendAsCommand(BSONObjBuilder* builder,
                                        const NamespaceString& nss,
                                        const ChunkVersion& shardVersion,
                                        const ConnectionString& configServerConnectionString,
-                                       const std::string& fromShardId,
-                                       const std::string& toShardId,
+                                       const ShardId& fromShardId,
+                                       const ShardId& toShardId,
                                        const ChunkRange& range,
                                        int64_t maxChunkSizeBytes,
                                        const MigrationSecondaryThrottleOptions& secondaryThrottle,
@@ -145,8 +149,8 @@ void MoveChunkRequest::appendAsCommand(BSONObjBuilder* builder,
     builder->append(kMoveChunk, nss.ns());
     shardVersion.appendForCommands(builder);
     builder->append(kConfigServerConnectionString, configServerConnectionString.toString());
-    builder->append(kFromShardId, fromShardId);
-    builder->append(kToShardId, toShardId);
+    builder->append(kFromShardId, fromShardId.toString());
+    builder->append(kToShardId, toShardId.toString());
     range.append(builder);
     builder->append(kMaxChunkSizeBytes, static_cast<long long>(maxChunkSizeBytes));
     secondaryThrottle.append(builder);
diff --git a/src/mongo/s/move_chunk_request.h b/src/mongo/s/move_chunk_request.h
index 3cbb4101c1a..7004dc99b92 100644
--- a/src/mongo/s/move_chunk_request.h
+++ b/src/mongo/s/move_chunk_request.h
@@ -66,8 +66,8 @@ public:
                                 const NamespaceString& nss,
                                 const ChunkVersion& shardVersion,
                                 const ConnectionString& configServerConnectionString,
-                                const std::string& fromShardId,
-                                const std::string& toShardId,
+                                const ShardId& fromShardId,
+                                const ShardId& toShardId,
                                 const ChunkRange& range,
                                 int64_t maxChunkSizeBytes,
                                 const MigrationSecondaryThrottleOptions& secondaryThrottle,
@@ -82,11 +82,11 @@ public:
         return _configServerCS;
     }
 
-    const std::string& getFromShardId() const {
+    const ShardId& getFromShardId() const {
         return _fromShardId;
     }
 
-    const std::string& getToShardId() const {
+    const ShardId& getToShardId() const {
         return _toShardId;
     }
 
@@ -135,10 +135,10 @@ private:
     ConnectionString _configServerCS;
 
     // The source shard id
-    std::string _fromShardId;
+    ShardId _fromShardId;
 
     // The recipient shard id
-    std::string _toShardId;
+    ShardId _toShardId;
 
     // Range of chunk chunk being moved
     ChunkRange _range;
diff --git a/src/mongo/s/move_chunk_request_test.cpp b/src/mongo/s/move_chunk_request_test.cpp
index 7bf5d8b46a6..4b657e5215d 100644
--- a/src/mongo/s/move_chunk_request_test.cpp
+++ b/src/mongo/s/move_chunk_request_test.cpp
@@ -46,8 +46,8 @@ TEST(MoveChunkRequest, CreateAsCommandComplete) {
         NamespaceString("TestDB", "TestColl"),
         ChunkVersion(2, 3, OID::gen()),
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
-        "shard0001",
-        "shard0002",
+        ShardId("shard0001"),
+        ShardId("shard0002"),
         ChunkRange(BSON("Key" << -100), BSON("Key" << 100)),
         1024,
         MigrationSecondaryThrottleOptions::create(MigrationSecondaryThrottleOptions::kOff),
@@ -60,8 +60,8 @@ TEST(MoveChunkRequest, CreateAsCommandComplete) {
         MoveChunkRequest::createFromCommand(NamespaceString(cmdObj["moveChunk"].String()), cmdObj));
     ASSERT_EQ("TestDB.TestColl", request.getNss().ns());
     ASSERT_EQ("TestConfigRS/CS1:12345,CS2:12345,CS3:12345", request.getConfigServerCS().toString());
-    ASSERT_EQ("shard0001", request.getFromShardId());
-    ASSERT_EQ("shard0002", request.getToShardId());
+    ASSERT_EQ(ShardId("shard0001"), request.getFromShardId());
+    ASSERT_EQ(ShardId("shard0002"), request.getToShardId());
     ASSERT_EQ(BSON("Key" << -100), request.getMinKey());
     ASSERT_EQ(BSON("Key" << 100), request.getMaxKey());
     ASSERT_EQ(1024, request.getMaxChunkSizeBytes());
@@ -78,8 +78,8 @@ TEST(MoveChunkRequest, EqualityOperatorSameValue) {
         NamespaceString("TestDB", "TestColl"),
         ChunkVersion(2, 3, OID::gen()),
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
-        "shard0001",
-        "shard0002",
+        ShardId("shard0001"),
+        ShardId("shard0002"),
         ChunkRange(BSON("Key" << -100), BSON("Key" << 100)),
         1024,
         MigrationSecondaryThrottleOptions::create(MigrationSecondaryThrottleOptions::kOff),
@@ -104,8 +104,8 @@ TEST(MoveChunkRequest, EqualityOperatorDifferentValues) {
         NamespaceString("TestDB", "TestColl"),
         ChunkVersion(2, 3, OID::gen()),
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
-        "shard0001",
-        "shard0002",
+        ShardId("shard0001"),
+        ShardId("shard0002"),
         ChunkRange(BSON("Key" << -100), BSON("Key" << 100)),
         1024,
         MigrationSecondaryThrottleOptions::create(MigrationSecondaryThrottleOptions::kOff),
@@ -121,8 +121,8 @@ TEST(MoveChunkRequest, EqualityOperatorDifferentValues) {
         NamespaceString("TestDB", "TestColl"),
         ChunkVersion(2, 3, OID::gen()),
         assertGet(ConnectionString::parse("TestConfigRS/CS1:12345,CS2:12345,CS3:12345")),
-        "shard0001",
-        "shard0002",
+        ShardId("shard0001"),
+        ShardId("shard0002"),
         ChunkRange(BSON("Key" << 100), BSON("Key" << 200)),  // Different key ranges
         1024,
         MigrationSecondaryThrottleOptions::create(MigrationSecondaryThrottleOptions::kOff),
diff --git a/src/mongo/s/ns_targeter.h b/src/mongo/s/ns_targeter.h
index 23bb6656f52..62fd02e5e22 100644
--- a/src/mongo/s/ns_targeter.h
+++ b/src/mongo/s/ns_targeter.h
@@ -35,6 +35,7 @@
 #include "mongo/client/dbclientinterface.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/s/chunk_version.h"
+#include "mongo/s/shard_id.h"
 #include "mongo/s/write_ops/batched_delete_document.h"
 #include "mongo/s/write_ops/batched_update_document.h"
 
@@ -157,10 +158,10 @@ struct ShardEndpoint {
     ShardEndpoint(const ShardEndpoint& other)
         : shardName(other.shardName), shardVersion(other.shardVersion) {}
 
-    ShardEndpoint(const std::string& shardName, const ChunkVersion& shardVersion)
+    ShardEndpoint(const ShardId& shardName, const ChunkVersion& shardVersion)
         : shardName(shardName), shardVersion(shardVersion) {}
 
-    const std::string shardName;
+    const ShardId shardName;
     const ChunkVersion shardVersion;
 };
 
diff --git a/src/mongo/s/query/async_results_merger_test.cpp b/src/mongo/s/query/async_results_merger_test.cpp
index fc5a8989a61..b6893c076ea 100644
--- a/src/mongo/s/query/async_results_merger_test.cpp
+++ b/src/mongo/s/query/async_results_merger_test.cpp
@@ -55,7 +55,8 @@ using executor::RemoteCommandRequest;
 using executor::RemoteCommandResponse;
 
 const HostAndPort kTestConfigShardHost = HostAndPort("FakeConfigHost", 12345);
-const std::vector<std::string> kTestShardIds = {"FakeShard1", "FakeShard2", "FakeShard3"};
+const std::vector<ShardId> kTestShardIds = {
+    ShardId("FakeShard1"), ShardId("FakeShard2"), ShardId("FakeShard3")};
 const std::vector<HostAndPort> kTestShardHosts = {HostAndPort("FakeShard1Host", 12345),
                                                   HostAndPort("FakeShard2Host", 12345),
                                                   HostAndPort("FakeShard3Host", 12345)};
@@ -74,7 +75,7 @@ public:
 
         for (size_t i = 0; i < kTestShardIds.size(); i++) {
             ShardType shardType;
-            shardType.setName(kTestShardIds[i]);
+            shardType.setName(kTestShardIds[i].toString());
             shardType.setHost(kTestShardHosts[i].toString());
 
             shards.push_back(shardType);
diff --git a/src/mongo/s/request_types/balance_chunk_request_test.cpp b/src/mongo/s/request_types/balance_chunk_request_test.cpp
index 7aa51b14482..e39fdf90674 100644
--- a/src/mongo/s/request_types/balance_chunk_request_test.cpp
+++ b/src/mongo/s/request_types/balance_chunk_request_test.cpp
@@ -60,7 +60,7 @@ TEST(BalanceChunkRequest, ParseFromConfigCommandNoSecondaryThrottle) {
     ASSERT_EQ("TestDB.TestColl", chunk.getNS());
     ASSERT_EQ(BSON("a" << -100LL), chunk.getMin());
     ASSERT_EQ(BSON("a" << 100LL), chunk.getMax());
-    ASSERT_EQ("TestShard0000", chunk.getShard());
+    ASSERT_EQ(ShardId("TestShard0000"), chunk.getShard());
     ASSERT_EQ(version, chunk.getVersion());
 
     const auto& secondaryThrottle = request.getSecondaryThrottle();
@@ -90,7 +90,7 @@ TEST(BalanceChunkRequest, ParseFromConfigCommandWithSecondaryThrottle) {
     ASSERT_EQ("TestDB.TestColl", chunk.getNS());
     ASSERT_EQ(BSON("a" << -100LL), chunk.getMin());
     ASSERT_EQ(BSON("a" << 100LL), chunk.getMax());
-    ASSERT_EQ("TestShard0000", chunk.getShard());
+    ASSERT_EQ(ShardId("TestShard0000"), chunk.getShard());
     ASSERT_EQ(version, chunk.getVersion());
 
     const auto& secondaryThrottle = request.getSecondaryThrottle();
diff --git a/src/mongo/s/request_types/balance_chunk_request_type.cpp b/src/mongo/s/request_types/balance_chunk_request_type.cpp
index 77b0e794eac..806f08f71fe 100644
--- a/src/mongo/s/request_types/balance_chunk_request_type.cpp
+++ b/src/mongo/s/request_types/balance_chunk_request_type.cpp
@@ -127,7 +127,7 @@ BSONObj BalanceChunkRequest::serializeToMoveCommandForConfig(
     BSONObjBuilder cmdBuilder;
     cmdBuilder.append(kConfigSvrMoveChunk, 1);
     cmdBuilder.appendElements(chunk.toBSON());
-    cmdBuilder.append(kToShardId, newShardId);
+    cmdBuilder.append(kToShardId, newShardId.toString());
     cmdBuilder.append(kMaxChunkSizeBytes, static_cast<long long>(maxChunkSizeBytes));
     {
         BSONObjBuilder secondaryThrottleBuilder(cmdBuilder.subobjStart(kSecondaryThrottle));
diff --git a/src/mongo/s/set_shard_version_request.cpp b/src/mongo/s/set_shard_version_request.cpp
index b21c4423a84..979a5f5f915 100644
--- a/src/mongo/s/set_shard_version_request.cpp
+++ b/src/mongo/s/set_shard_version_request.cpp
@@ -52,7 +52,7 @@ const char kNoConnectionVersioning[] = "noConnectionVersioning";
 }  // namespace
 
 SetShardVersionRequest::SetShardVersionRequest(ConnectionString configServer,
-                                               std::string shardName,
+                                               ShardId shardName,
                                                ConnectionString shardConnectionString)
     : _init(true),
       _isAuthoritative(true),
@@ -61,7 +61,7 @@ SetShardVersionRequest::SetShardVersionRequest(ConnectionString configServer,
       _shardCS(std::move(shardConnectionString)) {}
 
 SetShardVersionRequest::SetShardVersionRequest(ConnectionString configServer,
-                                               std::string shardName,
+                                               ShardId shardName,
                                                ConnectionString shardConnectionString,
                                                NamespaceString nss,
                                                ChunkVersion version,
@@ -78,14 +78,14 @@ SetShardVersionRequest::SetShardVersionRequest() = default;
 
 SetShardVersionRequest SetShardVersionRequest::makeForInit(
     const ConnectionString& configServer,
-    const std::string& shardName,
+    const ShardId& shardName,
     const ConnectionString& shardConnectionString) {
     return SetShardVersionRequest(configServer, shardName, shardConnectionString);
 }
 
 SetShardVersionRequest SetShardVersionRequest::makeForInitNoPersist(
     const ConnectionString& configServer,
-    const std::string& shardName,
+    const ShardId& shardName,
     const ConnectionString& shardConnectionString) {
     auto ssv = SetShardVersionRequest(configServer, shardName, shardConnectionString);
     ssv._noConnectionVersioning = true;
@@ -94,7 +94,7 @@ SetShardVersionRequest SetShardVersionRequest::makeForInitNoPersist(
 
 SetShardVersionRequest SetShardVersionRequest::makeForVersioning(
     const ConnectionString& configServer,
-    const std::string& shardName,
+    const ShardId& shardName,
     const ConnectionString& shardConnectionString,
     const NamespaceString& nss,
     const ChunkVersion& nssVersion,
@@ -106,7 +106,7 @@ SetShardVersionRequest SetShardVersionRequest::makeForVersioning(
 
 SetShardVersionRequest SetShardVersionRequest::makeForVersioningNoPersist(
     const ConnectionString& configServer,
-    const std::string& shardName,
+    const ShardId& shardName,
     const ConnectionString& shard,
     const NamespaceString& nss,
     const ChunkVersion& nssVersion,
@@ -134,7 +134,10 @@ StatusWith<SetShardVersionRequest> SetShardVersionRequest::parseFromBSON(const B
     }
 
     {
-        Status status = bsonExtractStringField(cmdObj, kShardName, &request._shardName);
+        std::string shardName;
+        Status status = bsonExtractStringField(cmdObj, kShardName, &shardName);
+        request._shardName = ShardId(shardName);
+
         if (!status.isOK())
             return status;
     }
@@ -212,7 +215,7 @@ BSONObj SetShardVersionRequest::toBSON() const {
     cmdBuilder.append(kInit, _init);
     cmdBuilder.append(kAuthoritative, _isAuthoritative);
     cmdBuilder.append(kConfigServer, _configServer.toString());
-    cmdBuilder.append(kShardName, _shardName);
+    cmdBuilder.append(kShardName, _shardName.toString());
     cmdBuilder.append(kShardConnectionString, _shardCS.toString());
 
     if (_init) {
diff --git a/src/mongo/s/set_shard_version_request.h b/src/mongo/s/set_shard_version_request.h
index af86db021e9..857866a36a9 100644
--- a/src/mongo/s/set_shard_version_request.h
+++ b/src/mongo/s/set_shard_version_request.h
@@ -34,6 +34,7 @@
 #include "mongo/client/connection_string.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/s/chunk_version.h"
+#include "mongo/s/shard_id.h"
 
 namespace mongo {
 
@@ -55,7 +56,7 @@ public:
      * are marked as sharded.
      */
     static SetShardVersionRequest makeForInit(const ConnectionString& configServer,
-                                              const std::string& shardName,
+                                              const ShardId& shardName,
                                               const ConnectionString& shardConnectionString);
 
     /**
@@ -68,7 +69,7 @@ public:
      */
     static SetShardVersionRequest makeForInitNoPersist(
         const ConnectionString& configServer,
-        const std::string& shardName,
+        const ShardId& shardName,
         const ConnectionString& shardConnectionString);
 
     /**
@@ -81,7 +82,7 @@ public:
      * are marked as sharded.
      */
     static SetShardVersionRequest makeForVersioning(const ConnectionString& configServer,
-                                                    const std::string& shardName,
+                                                    const ShardId& shardName,
                                                     const ConnectionString& shard,
                                                     const NamespaceString& nss,
                                                     const ChunkVersion& nssVersion,
@@ -96,7 +97,7 @@ public:
      * marked as sharded.
      */
     static SetShardVersionRequest makeForVersioningNoPersist(const ConnectionString& configServer,
-                                                             const std::string& shardName,
+                                                             const ShardId& shardName,
                                                              const ConnectionString& shard,
                                                              const NamespaceString& nss,
                                                              const ChunkVersion& nssVersion,
@@ -134,7 +135,7 @@ public:
         return _configServer;
     }
 
-    const std::string& getShardName() const {
+    const ShardId& getShardName() const {
         return _shardName;
     }
 
@@ -164,11 +165,11 @@ public:
 
 private:
     SetShardVersionRequest(ConnectionString configServer,
-                           std::string shardName,
+                           ShardId shardName,
                            ConnectionString shardConnectionString);
 
     SetShardVersionRequest(ConnectionString configServer,
-                           std::string shardName,
+                           ShardId shardName,
                            ConnectionString shardConnectionString,
                            NamespaceString nss,
                            ChunkVersion version,
@@ -182,7 +183,7 @@ private:
 
     ConnectionString _configServer;
 
-    std::string _shardName;
+    ShardId _shardName;
     ConnectionString _shardCS;
 
     // These values are only set if _init is false
diff --git a/src/mongo/s/set_shard_version_request_test.cpp b/src/mongo/s/set_shard_version_request_test.cpp
index 794d8bb552c..776a8e00c8f 100644
--- a/src/mongo/s/set_shard_version_request_test.cpp
+++ b/src/mongo/s/set_shard_version_request_test.cpp
@@ -258,7 +258,7 @@ TEST(SetShardVersionRequest, ParseFullNSContainsDBOnly) {
 
 TEST(SetShardVersionRequest, ToSSVCommandInit) {
     SetShardVersionRequest ssv =
-        SetShardVersionRequest::makeForInit(configCS, "TestShard", shardCS);
+        SetShardVersionRequest::makeForInit(configCS, ShardId("TestShard"), shardCS);
 
     ASSERT(ssv.isInit());
     ASSERT(ssv.isAuthoritative());
@@ -286,7 +286,7 @@ TEST(SetShardVersionRequest, ToSSVCommandInit) {
 
 TEST(SetShardVersionRequest, ToSSVCommandInitNoConnectionVersioning) {
     SetShardVersionRequest ssv =
-        SetShardVersionRequest::makeForInitNoPersist(configCS, "TestShard", shardCS);
+        SetShardVersionRequest::makeForInitNoPersist(configCS, ShardId("TestShard"), shardCS);
 
     ASSERT(ssv.isInit());
     ASSERT(ssv.isAuthoritative());
@@ -318,7 +318,7 @@ TEST(SetShardVersionRequest, ToSSVCommandFull) {
     const ChunkVersion chunkVersion(1, 2, OID::gen());
 
     SetShardVersionRequest ssv = SetShardVersionRequest::makeForVersioning(
-        configCS, "TestShard", shardCS, NamespaceString("db.coll"), chunkVersion, false);
+        configCS, ShardId("TestShard"), shardCS, NamespaceString("db.coll"), chunkVersion, false);
 
     ASSERT(!ssv.isInit());
     ASSERT(!ssv.isAuthoritative());
@@ -353,7 +353,7 @@ TEST(SetShardVersionRequest, ToSSVCommandFullAuthoritative) {
     const ChunkVersion chunkVersion(1, 2, OID::gen());
 
     SetShardVersionRequest ssv = SetShardVersionRequest::makeForVersioning(
-        configCS, "TestShard", shardCS, NamespaceString("db.coll"), chunkVersion, true);
+        configCS, ShardId("TestShard"), shardCS, NamespaceString("db.coll"), chunkVersion, true);
 
     ASSERT(!ssv.isInit());
     ASSERT(ssv.isAuthoritative());
@@ -388,7 +388,7 @@ TEST(SetShardVersionRequest, ToSSVCommandFullNoConnectionVersioning) {
     const ChunkVersion chunkVersion(1, 2, OID::gen());
 
     SetShardVersionRequest ssv = SetShardVersionRequest::makeForVersioningNoPersist(
-        configCS, "TestShard", shardCS, NamespaceString("db.coll"), chunkVersion, true);
+        configCS, ShardId("TestShard"), shardCS, NamespaceString("db.coll"), chunkVersion, true);
 
     ASSERT(!ssv.isInit());
     ASSERT(ssv.isAuthoritative());
diff --git a/src/mongo/s/shard_id.cpp b/src/mongo/s/shard_id.cpp
new file mode 100644
index 00000000000..961c8711e17
--- /dev/null
+++ b/src/mongo/s/shard_id.cpp
@@ -0,0 +1,88 @@
+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
+
+#include "mongo/platform/basic.h"
+
+#include <functional>
+#include <string.h>
+
+#include "mongo/base/status_with.h"
+#include "mongo/s/shard_id.h"
+
+namespace mongo {
+
+using std::string;
+using std::ostream;
+
+bool ShardId::operator==(const ShardId& other) const {
+    return (this->_shardId == other._shardId);
+}
+
+bool ShardId::operator!=(const ShardId& other) const {
+    return !(*this == other);
+}
+
+bool ShardId::operator==(const string& other) const {
+    return (this->_shardId == other);
+}
+
+bool ShardId::operator!=(const string& other) const {
+    return !(*this == other);
+}
+
+ShardId::operator StringData() {
+    return StringData(_shardId.data(), _shardId.size());
+}
+
+const string& ShardId::toString() const {
+    return _shardId;
+}
+
+bool ShardId::isValid() const {
+    return !_shardId.empty();
+}
+
+ostream& operator<<(ostream& os, const ShardId& shardId) {
+    os << shardId._shardId;
+    return os;
+}
+
+bool ShardId::operator<(const ShardId& other) const {
+    return _shardId < other._shardId;
+}
+
+int ShardId::compare(const ShardId& other) const {
+    return _shardId.compare(other._shardId);
+}
+
+std::size_t ShardId::Hasher::operator()(const ShardId& shardId) const {
+    return std::hash<std::string>()(shardId._shardId);
+}
+}  // namespace mongo
diff --git a/src/mongo/s/shard_id.h b/src/mongo/s/shard_id.h
new file mode 100644
index 00000000000..6456fc41677
--- /dev/null
+++ b/src/mongo/s/shard_id.h
@@ -0,0 +1,105 @@
+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <iostream>
+#include <string>
+
+#include "mongo/base/string_data.h"
+#include "mongo/bson/util/builder.h"
+
+
+namespace mongo {
+
+class NamespaceString;
+
+/**
+ *  Representation of a shard identifier.
+ */
+class ShardId {
+public:
+    friend std::ostream& operator<<(std::ostream&, const ShardId&);
+
+    ShardId() = default;
+
+    // Note that this c-tor allows the implicit conversion from std::string
+    ShardId(const std::string shardId) : _shardId(std::move(shardId)) {}
+
+    // Implicit StringData conversion
+    operator StringData();
+
+    bool operator==(const ShardId&) const;
+    bool operator!=(const ShardId&) const;
+    bool operator==(const std::string&) const;
+    bool operator!=(const std::string&) const;
+
+    template <size_t N>
+    bool operator==(const char (&val)[N]) const {
+        return (strncmp(val, _shardId.data(), N) == 0);
+    }
+
+    template <size_t N>
+    bool operator!=(const char (&val)[N]) const {
+        return (strncmp(val, _shardId.data(), N) != 0);
+    }
+
+    // The operator<  is needed to do proper comparison in a std::map
+    bool operator<(const ShardId&) const;
+
+    const std::string& toString() const;
+
+    /**
+     * Returns -1, 0, or 1 if 'this' is less, equal, or greater than 'other' in
+     * lexicographical order.
+     */
+    int compare(const ShardId& other) const;
+
+    /**
+     *  Returns true if _shardId is empty. Subject to include more validations in the future.
+     */
+    bool isValid() const;
+
+    /**
+     * Functor compatible with std::hash for std::unordered_{map,set}
+     */
+    struct Hasher {
+        std::size_t operator()(const ShardId&) const;
+    };
+
+private:
+    std::string _shardId;
+};
+
+template <typename Allocator>
+StringBuilderImpl<Allocator>& operator<<(StringBuilderImpl<Allocator>& stream,
+                                         const ShardId& shardId) {
+    return stream << shardId.toString();
+}
+
+}  // namespace mongo
diff --git a/src/mongo/s/shard_id_test.cpp b/src/mongo/s/shard_id_test.cpp
new file mode 100644
index 00000000000..6393c9e9a9e
--- /dev/null
+++ b/src/mongo/s/shard_id_test.cpp
@@ -0,0 +1,107 @@
+/*    Copyright 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#include "mongo/s/shard_id.h"
+
+#include "mongo/base/string_data.h"
+#include "mongo/platform/basic.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+using std::string;
+using namespace mongo;
+
+TEST(ShardId, Valid) {
+    ShardId shardId("my_shard_id");
+    ASSERT(shardId.isValid());
+}
+
+TEST(ShardId, Invalid) {
+    ShardId shardId("");
+    ASSERT(!shardId.isValid());
+}
+
+TEST(ShardId, Roundtrip) {
+    string shard_id_str("my_shard_id");
+    ShardId shardId(shard_id_str);
+    ASSERT(shard_id_str == shardId.toString());
+}
+
+TEST(ShardId, ToStringData) {
+    string shard_id_str("my_shard_id");
+    ShardId shardId(shard_id_str);
+    StringData stringData(shardId);
+    ASSERT(stringData == shard_id_str);
+}
+
+TEST(ShardId, Assign) {
+    ShardId shardId1("my_shard_id");
+    auto shardId2 = shardId1;
+    ASSERT(shardId1 == shardId2);
+}
+
+TEST(ShardId, Less) {
+    string a("aaa");
+    string a1("aaa");
+    string b("bbb");
+    ShardId sa(a);
+    ShardId sa1(a1);
+    ShardId sb(b);
+    ASSERT_EQUALS(sa < sa1, a < a1);
+    ASSERT_EQUALS(sb < sa1, b < a1);
+    ASSERT_EQUALS(sa < sb, a < b);
+}
+
+TEST(ShardId, Compare) {
+    string a("aaa");
+    string a1("aaa");
+    string b("bbb");
+    ShardId sa(a);
+    ShardId sa1(a1);
+    ShardId sb(b);
+    ASSERT_EQUALS(sa.compare(sa1), a.compare(a1));
+    ASSERT_EQUALS(sb.compare(sa1), b.compare(a1));
+    ASSERT_EQUALS(sa.compare(sb), a.compare(b));
+}
+
+TEST(ShardId, Equals) {
+    string a("aaa");
+    string a1("aaa");
+    string b("bbb");
+    ShardId sa(a);
+    ShardId sa1(a1);
+    ShardId sb(b);
+    ASSERT(sa == sa1);
+    ASSERT(sa != sb);
+    ASSERT(sa == "aaa");
+    ASSERT(sa != "bbb");
+}
+
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/s/shard_util.cpp b/src/mongo/s/shard_util.cpp
index 7b96fb78239..61f90ab9588 100644
--- a/src/mongo/s/shard_util.cpp
+++ b/src/mongo/s/shard_util.cpp
@@ -191,7 +191,7 @@ StatusWith<boost::optional<ChunkRange>> splitChunkAtMultiplePoints(
     cmd.append("splitChunk", nss.ns());
     cmd.append("configdb",
                Grid::get(txn)->shardRegistry()->getConfigServerConnectionString().toString());
-    cmd.append("from", shardId);
+    cmd.append("from", shardId.toString());
     cmd.append("keyPattern", shardKeyPattern.toBSON());
     collectionVersion.appendForCommands(&cmd);
     cmd.append(kMinKey, minKey);
diff --git a/src/mongo/s/write_ops/batch_write_op_test.cpp b/src/mongo/s/write_ops/batch_write_op_test.cpp
index a20f5c98f47..01513e0eb76 100644
--- a/src/mongo/s/write_ops/batch_write_op_test.cpp
+++ b/src/mongo/s/write_ops/batch_write_op_test.cpp
@@ -137,7 +137,7 @@ TEST(WriteOpTests, SingleOp) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -177,7 +177,7 @@ TEST(WriteOpTests, SingleError) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -223,7 +223,7 @@ TEST(WriteOpTests, SingleTargetError) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterHalfRange(nss, endpoint, &targeter);
 
@@ -266,7 +266,7 @@ TEST(WriteOpTests, SingleWriteConcernErrorOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -316,7 +316,7 @@ TEST(WriteOpTests, SingleStaleError) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -383,7 +383,7 @@ TEST(WriteOpTests, MultiOpSameShardOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -427,7 +427,7 @@ TEST(WriteOpTests, MultiOpSameShardUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -472,8 +472,8 @@ TEST(WriteOpTests, MultiOpTwoShardsOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -531,8 +531,8 @@ TEST(WriteOpTests, MultiOpTwoShardsUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -583,8 +583,8 @@ TEST(WriteOpTests, MultiOpTwoShardsEachOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -654,8 +654,8 @@ TEST(WriteOpTests, MultiOpTwoShardsEachUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -710,8 +710,8 @@ TEST(WriteOpTests, MultiOpOneOrTwoShardsOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -822,8 +822,8 @@ TEST(WriteOpTests, MultiOpOneOrTwoShardsUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -884,8 +884,8 @@ TEST(WriteOpTests, MultiOpSingleShardErrorUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -948,8 +948,8 @@ TEST(WriteOpTests, MultiOpTwoShardErrorsUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1015,8 +1015,8 @@ TEST(WriteOpTests, MultiOpPartialSingleShardErrorUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1082,8 +1082,8 @@ TEST(WriteOpTests, MultiOpPartialSingleShardErrorOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1153,7 +1153,7 @@ TEST(WriteOpTests, MultiOpErrorAndWriteConcernErrorUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -1197,8 +1197,8 @@ TEST(WriteOpTests, SingleOpErrorAndWriteConcernErrorOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1248,7 +1248,7 @@ TEST(WriteOpTests, MultiOpFailedTargetOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterHalfRange(nss, endpoint, &targeter);
 
@@ -1311,7 +1311,7 @@ TEST(WriteOpTests, MultiOpFailedTargetUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterHalfRange(nss, endpoint, &targeter);
 
@@ -1368,8 +1368,8 @@ TEST(WriteOpTests, MultiOpFailedBatchOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1421,8 +1421,8 @@ TEST(WriteOpTests, MultiOpFailedBatchUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1474,8 +1474,8 @@ TEST(WriteOpTests, MultiOpAbortOrdered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1524,8 +1524,8 @@ TEST(WriteOpTests, MultiOpAbortUnordered) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1565,8 +1565,8 @@ TEST(WriteOpTests, MultiOpTwoWCErrors) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpointA("shardA", ChunkVersion::IGNORED());
-    ShardEndpoint endpointB("shardB", ChunkVersion::IGNORED());
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion::IGNORED());
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterSplitRange(nss, endpointA, endpointB, &targeter);
 
@@ -1617,7 +1617,7 @@ TEST(WriteOpLimitTests, OneBigDoc) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -1652,7 +1652,7 @@ TEST(WriteOpLimitTests, OneBigOneSmall) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -1699,7 +1699,7 @@ TEST(WriteOpLimitTests, TooManyOps) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
@@ -1745,7 +1745,7 @@ TEST(WriteOpLimitTests, UpdateOverheadIncluded) {
 
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
     MockNSTargeter targeter;
     initTargeterFullRange(nss, endpoint, &targeter);
 
diff --git a/src/mongo/s/write_ops/write_op_test.cpp b/src/mongo/s/write_ops/write_op_test.cpp
index e488c068e47..1f43d6188be 100644
--- a/src/mongo/s/write_ops/write_op_test.cpp
+++ b/src/mongo/s/write_ops/write_op_test.cpp
@@ -86,7 +86,7 @@ TEST(WriteOpTests, TargetSingle) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpoint, nss, BSON("x" << MINKEY), BSON("x" << MAXKEY)));
@@ -144,9 +144,9 @@ TEST(WriteOpTests, TargetMultiOneShard) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpointA("shardA", ChunkVersion(10, 0, OID()));
-    ShardEndpoint endpointB("shardB", ChunkVersion(20, 0, OID()));
-    ShardEndpoint endpointC("shardB", ChunkVersion(20, 0, OID()));
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion(10, 0, OID()));
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion(20, 0, OID()));
+    ShardEndpoint endpointC(ShardId("shardB"), ChunkVersion(20, 0, OID()));
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpointA, nss, BSON("x" << MINKEY), BSON("x" << 0)));
@@ -187,9 +187,9 @@ TEST(WriteOpTests, TargetMultiAllShards) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpointA("shardA", ChunkVersion(10, 0, OID()));
-    ShardEndpoint endpointB("shardB", ChunkVersion(20, 0, OID()));
-    ShardEndpoint endpointC("shardB", ChunkVersion(20, 0, OID()));
+    ShardEndpoint endpointA(ShardId("shardA"), ChunkVersion(10, 0, OID()));
+    ShardEndpoint endpointB(ShardId("shardB"), ChunkVersion(20, 0, OID()));
+    ShardEndpoint endpointC(ShardId("shardB"), ChunkVersion(20, 0, OID()));
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpointA, nss, BSON("x" << MINKEY), BSON("x" << 0)));
@@ -239,7 +239,7 @@ TEST(WriteOpTests, ErrorSingle) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpoint, nss, BSON("x" << MINKEY), BSON("x" << MAXKEY)));
@@ -285,7 +285,7 @@ TEST(WriteOpTests, CancelSingle) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpoint, nss, BSON("x" << MINKEY), BSON("x" << MAXKEY)));
@@ -328,7 +328,7 @@ TEST(WriteOpTests, RetrySingleOp) {
     OperationContextNoop txn;
     NamespaceString nss("foo.bar");
 
-    ShardEndpoint endpoint("shard", ChunkVersion::IGNORED());
+    ShardEndpoint endpoint(ShardId("shard"), ChunkVersion::IGNORED());
 
     vector<MockRange*> mockRanges;
     mockRanges.push_back(new MockRange(endpoint, nss, BSON("x" << MINKEY), BSON("x" << MAXKEY)));