SERVER-23996 ShardRegistry::getShard should return a StatusWith<shared_ptr<Shard>>

38 files changed, 325 insertions, 235 deletions

diff --git a/src/mongo/client/parallel.cpp b/src/mongo/client/parallel.cpp
index 8fdacb5efaa..3fca978c745 100644
--- a/src/mongo/client/parallel.cpp
+++ b/src/mongo/client/parallel.cpp
@@ -397,7 +397,7 @@ void ParallelSortClusteredCursor::setupVersionAndHandleSlaveOk(
 
     // Setup conn
     if (!state->conn) {
-        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
+        const auto shard = uassertStatusOK(grid.shardRegistry()->getShard(txn, shardId));
         state->conn.reset(new ShardConnection(shard->getConnString(), ns.ns(), manager));
     }
 
@@ -945,7 +945,7 @@ void ParallelSortClusteredCursor::finishInit(OperationContext* txn) {
         _cursors[index].reset(mdata.pcState->cursor.get(), &mdata);
 
         {
-            const auto shard = grid.shardRegistry()->getShard(txn, i->first);
+            const auto shard = uassertStatusOK(grid.shardRegistry()->getShard(txn, i->first));
             _servers.insert(shard->getConnString().toString());
         }
 
diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 9e61b381969..f25289baecd 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -1720,11 +1720,9 @@ public:
                 std::string server = e.fieldName();
                 servers.insert(server);
 
-                if (!grid.shardRegistry()->getShard(txn, server)) {
-                    return appendCommandStatus(
-                        result,
-                        Status(ErrorCodes::ShardNotFound,
-                               str::stream() << "Shard not found for server: " << server));
+                auto shardStatus = grid.shardRegistry()->getShard(txn, server);
+                if (!shardStatus.isOK()) {
+                    return appendCommandStatus(result, shardStatus.getStatus());
                 }
             }
         }
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 2a2d2e77d3e..a4ed3c77a7c 100644
--- a/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
+++ b/src/mongo/db/s/migration_chunk_cloner_source_legacy.cpp
@@ -184,12 +184,20 @@ Status MigrationChunkClonerSourceLegacy::startClone(OperationContext* txn) {
     // Resolve the donor and recipient shards and their connection string
 
     {
-        auto donorShard = grid.shardRegistry()->getShard(txn, _args.getFromShardId());
-        _donorCS = donorShard->getConnString();
+        auto donorShardStatus = grid.shardRegistry()->getShard(txn, _args.getFromShardId());
+        if (!donorShardStatus.isOK()) {
+            return donorShardStatus.getStatus();
+        }
+        _donorCS = donorShardStatus.getValue()->getConnString();
     }
 
     {
-        auto recipientShard = grid.shardRegistry()->getShard(txn, _args.getToShardId());
+        auto recipientShardStatus = grid.shardRegistry()->getShard(txn, _args.getToShardId());
+        if (!recipientShardStatus.isOK()) {
+            return recipientShardStatus.getStatus();
+        }
+        auto recipientShard = recipientShardStatus.getValue();
+
         auto shardHostStatus = recipientShard->getTargeter()->findHost(
             ReadPreferenceSetting{ReadPreference::PrimaryOnly});
         if (!shardHostStatus.isOK()) {
diff --git a/src/mongo/s/balancer/balancer.cpp b/src/mongo/s/balancer/balancer.cpp
index 77402222b2f..6296d42cb88 100644
--- a/src/mongo/s/balancer/balancer.cpp
+++ b/src/mongo/s/balancer/balancer.cpp
@@ -444,10 +444,11 @@ bool Balancer::_checkOIDs(OperationContext* txn) {
             return false;
         }
 
-        const auto s = shardingContext->shardRegistry()->getShard(txn, shardId);
-        if (!s) {
+        auto shardStatus = shardingContext->shardRegistry()->getShard(txn, shardId);
+        if (!shardStatus.isOK()) {
             continue;
         }
+        const auto s = shardStatus.getValue();
 
         auto result =
             uassertStatusOK(s->runCommand(txn,
@@ -474,14 +475,14 @@ bool Balancer::_checkOIDs(OperationContext* txn) {
                                   Shard::RetryPolicy::kIdempotent));
                 uassertStatusOK(result.commandStatus);
 
-                const auto otherShard = shardingContext->shardRegistry()->getShard(txn, oids[x]);
-                if (otherShard) {
-                    result = uassertStatusOK(
-                        otherShard->runCommand(txn,
-                                               ReadPreferenceSetting{ReadPreference::PrimaryOnly},
-                                               "admin",
-                                               BSON("features" << 1 << "oidReset" << 1),
-                                               Shard::RetryPolicy::kIdempotent));
+                auto otherShardStatus = shardingContext->shardRegistry()->getShard(txn, oids[x]);
+                if (otherShardStatus.isOK()) {
+                    result = uassertStatusOK(otherShardStatus.getValue()->runCommand(
+                        txn,
+                        ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+                        "admin",
+                        BSON("features" << 1 << "oidReset" << 1),
+                        Shard::RetryPolicy::kIdempotent));
                     uassertStatusOK(result.commandStatus);
                 }
 
diff --git a/src/mongo/s/balancer/cluster_statistics_impl.cpp b/src/mongo/s/balancer/cluster_statistics_impl.cpp
index 01993f1a938..8f229997cb2 100644
--- a/src/mongo/s/balancer/cluster_statistics_impl.cpp
+++ b/src/mongo/s/balancer/cluster_statistics_impl.cpp
@@ -62,10 +62,11 @@ const char kVersionField[] = "version";
  */
 StatusWith<string> retrieveShardMongoDVersion(OperationContext* txn, ShardId shardId) {
     auto shardRegistry = Grid::get(txn)->shardRegistry();
-    auto shard = shardRegistry->getShard(txn, shardId);
-    if (!shard) {
-        return {ErrorCodes::ShardNotFound, str::stream() << "shard " << shardId << " not found"};
+    auto shardStatus = shardRegistry->getShard(txn, shardId);
+    if (!shardStatus.isOK()) {
+        return shardStatus.getStatus();
     }
+    auto shard = shardStatus.getValue();
 
     auto commandResponse = shard->runCommand(txn,
                                              ReadPreferenceSetting{ReadPreference::PrimaryOnly},
diff --git a/src/mongo/s/balancer/migration_manager.cpp b/src/mongo/s/balancer/migration_manager.cpp
index 07d01481160..b73199ec848 100644
--- a/src/mongo/s/balancer/migration_manager.cpp
+++ b/src/mongo/s/balancer/migration_manager.cpp
@@ -320,7 +320,12 @@ shared_ptr<Notification<Status>> MigrationManager::_schedule(
                      << " does not exist."));
     }
 
-    const auto fromShard = Grid::get(txn)->shardRegistry()->getShard(txn, migrateInfo.from);
+    const auto fromShardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, migrateInfo.from);
+    if (!fromShardStatus.isOK()) {
+        return std::make_shared<Notification<Status>>(std::move(fromShardStatus.getStatus()));
+    }
+
+    const auto fromShard = fromShardStatus.getValue();
     auto fromHostStatus =
         fromShard->getTargeter()->findHost(ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                                            RemoteCommandTargeter::selectFindHostMaxWaitTime(txn));
diff --git a/src/mongo/s/balancer/migration_manager_test.cpp b/src/mongo/s/balancer/migration_manager_test.cpp
index fd06fdbc352..b4e9ab8e23c 100644
--- a/src/mongo/s/balancer/migration_manager_test.cpp
+++ b/src/mongo/s/balancer/migration_manager_test.cpp
@@ -159,7 +159,8 @@ void MigrationManagerTest::tearDown() {
 
 std::shared_ptr<RemoteCommandTargeterMock> MigrationManagerTest::shardTargeterMock(
     OperationContext* txn, ShardId shardId) {
-    return RemoteCommandTargeterMock::get(shardRegistry()->getShard(txn, shardId)->getTargeter());
+    return RemoteCommandTargeterMock::get(
+        uassertStatusOK(shardRegistry()->getShard(txn, shardId))->getTargeter());
 }
 
 void MigrationManagerTest::setUpDatabase(const std::string& dbName, const ShardId primaryShard) {
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 13379820db3..6f7315272ce 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_client_impl.cpp
@@ -419,7 +419,10 @@ Status ShardingCatalogClientImpl::shardCollection(OperationContext* txn,
     }
 
     ShardId dbPrimaryShardId = getDBStatus.getValue().value.getPrimary();
-    const auto primaryShard = grid.shardRegistry()->getShard(txn, dbPrimaryShardId);
+    const auto primaryShardStatus = grid.shardRegistry()->getShard(txn, dbPrimaryShardId);
+    if (!primaryShardStatus.isOK()) {
+        return primaryShardStatus.getStatus();
+    }
 
     {
         // In 3.0 and prior we include this extra safety check that the collection is not getting
@@ -446,7 +449,7 @@ Status ShardingCatalogClientImpl::shardCollection(OperationContext* txn,
         BSONObjBuilder collectionDetail;
         collectionDetail.append("shardKey", fieldsAndOrder.toBSON());
         collectionDetail.append("collection", ns);
-        collectionDetail.append("primary", primaryShard->toString());
+        collectionDetail.append("primary", primaryShardStatus.getValue()->toString());
 
         {
             BSONArrayBuilder initialShards(collectionDetail.subarrayStart("initShards"));
@@ -494,16 +497,16 @@ Status ShardingCatalogClientImpl::shardCollection(OperationContext* txn,
     SetShardVersionRequest ssv = SetShardVersionRequest::makeForVersioningNoPersist(
         grid.shardRegistry()->getConfigServerConnectionString(),
         dbPrimaryShardId,
-        primaryShard->getConnString(),
+        primaryShardStatus.getValue()->getConnString(),
         NamespaceString(ns),
         manager->getVersion(),
         true);
 
-    auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, dbPrimaryShardId);
-    if (!shard) {
-        return {ErrorCodes::ShardNotFound,
-                str::stream() << "shard " << dbPrimaryShardId << " not found"};
+    auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, dbPrimaryShardId);
+    if (!shardStatus.isOK()) {
+        return shardStatus.getStatus();
     }
+    auto shard = shardStatus.getValue();
 
     auto ssvResponse = shard->runCommand(txn,
                                          ReadPreferenceSetting{ReadPreference::PrimaryOnly},
@@ -808,18 +811,17 @@ Status ShardingCatalogClientImpl::dropCollection(OperationContext* txn, const Na
     auto* shardRegistry = grid.shardRegistry();
 
     for (const auto& shardEntry : allShards) {
-        auto shard = shardRegistry->getShard(txn, shardEntry.getName());
-        if (!shard) {
-            return {ErrorCodes::ShardNotFound,
-                    str::stream() << "shard " << shardEntry.getName() << " not found"};
+        auto shardStatus = shardRegistry->getShard(txn, shardEntry.getName());
+        if (!shardStatus.isOK()) {
+            return shardStatus.getStatus();
         }
-        auto dropResult =
-            shard->runCommand(txn,
-                              ReadPreferenceSetting{ReadPreference::PrimaryOnly},
-                              ns.db().toString(),
-                              BSON("drop" << ns.coll() << WriteConcernOptions::kWriteConcernField
-                                          << txn->getWriteConcern().toBSON()),
-                              Shard::RetryPolicy::kIdempotent);
+        auto dropResult = shardStatus.getValue()->runCommand(
+            txn,
+            ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+            ns.db().toString(),
+            BSON("drop" << ns.coll() << WriteConcernOptions::kWriteConcernField
+                        << txn->getWriteConcern().toBSON()),
+            Shard::RetryPolicy::kIdempotent);
 
         if (!dropResult.isOK()) {
             return Status(dropResult.getStatus().code(),
@@ -895,11 +897,11 @@ Status ShardingCatalogClientImpl::dropCollection(OperationContext* txn, const Na
             ChunkVersion::DROPPED(),
             true);
 
-        auto shard = shardRegistry->getShard(txn, shardEntry.getName());
-        if (!shard) {
-            return {ErrorCodes::ShardNotFound,
-                    str::stream() << "shard " << shardEntry.getName() << " not found"};
+        auto shardStatus = shardRegistry->getShard(txn, shardEntry.getName());
+        if (!shardStatus.isOK()) {
+            return shardStatus.getStatus();
         }
+        auto shard = shardStatus.getValue();
 
         auto ssvResult = shard->runCommand(txn,
                                            ReadPreferenceSetting{ReadPreference::PrimaryOnly},
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_drop_coll_test.cpp b/src/mongo/s/catalog/replset/sharding_catalog_drop_coll_test.cpp
index b62499cc355..b556bcb0672 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_drop_coll_test.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_drop_coll_test.cpp
@@ -79,11 +79,13 @@ public:
         setupShards({_shard1, _shard2});
 
         auto shard1Targeter = RemoteCommandTargeterMock::get(
-            shardRegistry()->getShard(operationContext(), _shard1.getName())->getTargeter());
+            uassertStatusOK(shardRegistry()->getShard(operationContext(), _shard1.getName()))
+                ->getTargeter());
         shard1Targeter->setFindHostReturnValue(HostAndPort(_shard1.getHost()));
 
         auto shard2Targeter = RemoteCommandTargeterMock::get(
-            shardRegistry()->getShard(operationContext(), _shard2.getName())->getTargeter());
+            uassertStatusOK(shardRegistry()->getShard(operationContext(), _shard2.getName()))
+                ->getTargeter());
         shard2Targeter->setFindHostReturnValue(HostAndPort(_shard2.getHost()));
     }
 
@@ -284,7 +286,8 @@ TEST_F(DropColl2ShardTest, DistLockBusy) {
 
 TEST_F(DropColl2ShardTest, FirstShardTargeterError) {
     auto shard1Targeter = RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), shard1().getName())->getTargeter());
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), shard1().getName()))
+            ->getTargeter());
     shard1Targeter->setFindHostReturnValue({ErrorCodes::HostUnreachable, "bad test network"});
 
     auto future = launchAsync([this] {
@@ -348,7 +351,8 @@ TEST_F(DropColl2ShardTest, FirstShardDropCmdError) {
 
 TEST_F(DropColl2ShardTest, SecondShardTargeterError) {
     auto shard2Targeter = RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), shard2().getName())->getTargeter());
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), shard2().getName()))
+            ->getTargeter());
     shard2Targeter->setFindHostReturnValue({ErrorCodes::HostUnreachable, "bad test network"});
 
     auto future = launchAsync([this] {
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_manager_impl.cpp b/src/mongo/s/catalog/replset/sharding_catalog_manager_impl.cpp
index 77dc96fd1fc..aac7bed4935 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_manager_impl.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_manager_impl.cpp
@@ -818,7 +818,7 @@ StatusWith<string> ShardingCatalogManagerImpl::addShard(
 
     // Ensure the added shard is visible to this process.
     auto shardRegistry = Grid::get(txn)->shardRegistry();
-    if (!shardRegistry->getShard(txn, shardType.getName())) {
+    if (!shardRegistry->getShard(txn, shardType.getName()).isOK()) {
         return {ErrorCodes::OperationFailed,
                 "Could not find shard metadata for shard after adding it. This most likely "
                 "indicates that the shard was removed immediately after it was added."};
@@ -1925,10 +1925,11 @@ Status ShardingCatalogManagerImpl::setFeatureCompatibilityVersionOnShards(
     std::vector<ShardId> shardIds;
     grid.shardRegistry()->getAllShardIds(&shardIds);
     for (const ShardId& shardId : shardIds) {
-        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
-        if (!shard) {
+        const auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+        if (!shardStatus.isOK()) {
             continue;
         }
+        const auto shard = shardStatus.getValue();
 
         auto response =
             shard->runCommand(txn,
diff --git a/src/mongo/s/catalog/replset/sharding_catalog_test.cpp b/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
index fab9b690c13..da4e375465f 100644
--- a/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
+++ b/src/mongo/s/catalog/replset/sharding_catalog_test.cpp
@@ -1564,16 +1564,15 @@ TEST_F(ShardingCatalogClientTest, createDatabaseSuccess) {
 
     // Set up all the target mocks return values.
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s0.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s0.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s0.getHost()));
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s1.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s1.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s1.getHost()));
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s2.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s2.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s2.getHost()));
 
-
     // Now actually start the createDatabase work.
 
     distLock()->expectLock([dbname](StringData name,
@@ -1855,16 +1854,15 @@ TEST_F(ShardingCatalogClientTest, createDatabaseDuplicateKeyOnInsert) {
 
     // Set up all the target mocks return values.
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s0.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s0.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s0.getHost()));
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s1.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s1.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s1.getHost()));
     RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), s2.getName())->getTargeter())
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), s2.getName()))->getTargeter())
         ->setFindHostReturnValue(HostAndPort(s2.getHost()));
 
-
     // Now actually start the createDatabase work.
 
     distLock()->expectLock([dbname](StringData name,
@@ -1977,7 +1975,8 @@ TEST_F(ShardingCatalogClientTest, EnableShardingNoDBExists) {
     setupShards(vector<ShardType>{shard});
 
     auto shardTargeter = RemoteCommandTargeterMock::get(
-        shardRegistry()->getShard(operationContext(), ShardId("shard0"))->getTargeter());
+        uassertStatusOK(shardRegistry()->getShard(operationContext(), ShardId("shard0")))
+            ->getTargeter());
     shardTargeter->setFindHostReturnValue(HostAndPort("shard0:12"));
 
     distLock()->expectLock(
diff --git a/src/mongo/s/chunk.cpp b/src/mongo/s/chunk.cpp
index c38dee72dd5..bcdd2dd09c7 100644
--- a/src/mongo/s/chunk.cpp
+++ b/src/mongo/s/chunk.cpp
@@ -81,7 +81,7 @@ Chunk::Chunk(OperationContext* txn, ChunkManager* manager, const ChunkType& from
     uassert(13327, "Chunk ns must match server ns", ns == _manager->getns());
     uassert(10172, "Chunk needs a min", !_min.isEmpty());
     uassert(10173, "Chunk needs a max", !_max.isEmpty());
-    uassert(10171, "Chunk needs a server", grid.shardRegistry()->getShard(txn, _shardId));
+    uassert(10171, "Chunk needs a server", grid.shardRegistry()->getShard(txn, _shardId).isOK());
 }
 
 Chunk::Chunk(ChunkManager* info,
@@ -415,7 +415,7 @@ bool Chunk::splitIfShould(OperationContext* txn, long dataWritten) {
 }
 
 ConnectionString Chunk::_getShardConnectionString(OperationContext* txn) const {
-    const auto shard = grid.shardRegistry()->getShard(txn, getShardId());
+    const auto shard = uassertStatusOK(grid.shardRegistry()->getShard(txn, getShardId()));
     return shard->getConnString();
 }
 
diff --git a/src/mongo/s/chunk_manager.cpp b/src/mongo/s/chunk_manager.cpp
index cda67a18e06..43bd27ee42f 100644
--- a/src/mongo/s/chunk_manager.cpp
+++ b/src/mongo/s/chunk_manager.cpp
@@ -102,7 +102,7 @@ public:
     }
 
     ShardId shardFor(OperationContext* txn, const ShardId& shardId) const final {
-        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
+        const auto shard = uassertStatusOK(grid.shardRegistry()->getShard(txn, shardId));
         return shard->getId();
     }
 
@@ -308,11 +308,12 @@ bool ChunkManager::_load(OperationContext* txn,
 
         // Add all existing shards we find to the shards set
         for (ShardVersionMap::iterator it = shardVersions->begin(); it != shardVersions->end();) {
-            shared_ptr<Shard> shard = grid.shardRegistry()->getShard(txn, it->first);
-            if (shard) {
+            auto shardStatus = grid.shardRegistry()->getShard(txn, it->first);
+            if (shardStatus.isOK()) {
                 shardIds.insert(it->first);
                 ++it;
             } else {
+                invariant(shardStatus == ErrorCodes::ShardNotFound);
                 shardVersions->erase(it++);
             }
         }
@@ -380,7 +381,7 @@ void ChunkManager::calcInitSplitsAndShards(OperationContext* txn,
 
     if (!initPoints || initPoints->empty()) {
         // discover split points
-        const auto primaryShard = grid.shardRegistry()->getShard(txn, primaryShardId);
+        auto primaryShard = uassertStatusOK(grid.shardRegistry()->getShard(txn, primaryShardId));
         const NamespaceString nss{getns()};
 
         auto result = uassertStatusOK(
diff --git a/src/mongo/s/client/shard_connection.cpp b/src/mongo/s/client/shard_connection.cpp
index a4faaa34377..7e38ed59b9e 100644
--- a/src/mongo/s/client/shard_connection.cpp
+++ b/src/mongo/s/client/shard_connection.cpp
@@ -281,10 +281,12 @@ public:
         // Now only check top-level shard connections
         for (const ShardId& shardId : all) {
             try {
-                const auto shard = grid.shardRegistry()->getShard(txn, shardId);
-                if (!shard) {
+                auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+                if (!shardStatus.isOK()) {
+                    invariant(shardStatus == ErrorCodes::ShardNotFound);
                     continue;
                 }
+                const auto shard = shardStatus.getValue();
 
                 string sconnString = shard->getConnString().toString();
                 Status* s = _getStatus(sconnString);
diff --git a/src/mongo/s/client/shard_registry.cpp b/src/mongo/s/client/shard_registry.cpp
index 7846cc8b560..3b98f4f7334 100644
--- a/src/mongo/s/client/shard_registry.cpp
+++ b/src/mongo/s/client/shard_registry.cpp
@@ -106,7 +106,8 @@ void ShardRegistry::rebuildConfigShard() {
     invariant(_data.getConfigShard());
 }
 
-shared_ptr<Shard> ShardRegistry::getShard(OperationContext* txn, const ShardId& shardId) {
+StatusWith<shared_ptr<Shard>> ShardRegistry::getShard(OperationContext* txn,
+                                                      const ShardId& shardId) {
     // If we know about the shard, return it.
     auto shard = _data.findByShardId(shardId);
     if (shard) {
@@ -117,16 +118,27 @@ shared_ptr<Shard> ShardRegistry::getShard(OperationContext* txn, const ShardId&
     bool didReload = reload(txn);
     shard = _data.findByShardId(shardId);
 
-    // If we found the shard, return it. If we did not find the shard but performed the reload
-    // ourselves, return, because it means the shard does not exist.
-    if (shard || didReload) {
+    // If we found the shard, return it.
+    if (shard) {
         return shard;
     }
 
+    // If we did not find the shard but performed the reload
+    // ourselves, return, because it means the shard does not exist.
+    if (didReload) {
+        return {ErrorCodes::ShardNotFound, str::stream() << "Shard " << shardId << " not found"};
+    }
+
     // If we did not perform the reload ourselves (because there was a concurrent reload), force a
     // reload again to ensure that we have seen data at least as up to date as our first reload.
     reload(txn);
-    return _data.findByShardId(shardId);
+    shard = _data.findByShardId(shardId);
+
+    if (shard) {
+        return shard;
+    }
+
+    return {ErrorCodes::ShardNotFound, str::stream() << "Shard " << shardId << " not found"};
 }
 
 shared_ptr<Shard> ShardRegistry::getShardNoReload(const ShardId& shardId) {
diff --git a/src/mongo/s/client/shard_registry.h b/src/mongo/s/client/shard_registry.h
index 61adaa20bac..edd78e8af02 100644
--- a/src/mongo/s/client/shard_registry.h
+++ b/src/mongo/s/client/shard_registry.h
@@ -185,12 +185,14 @@ public:
     void updateReplSetHosts(const ConnectionString& newConnString);
 
     /**
-     * Returns a shared pointer to the shard object with the given shard id.
+     * Returns a shared pointer to the shard object with the given shard id, or ShardNotFound error
+     * otherwise.
+     *
      * May refresh the shard registry if there's no cached information about the shard. The shardId
      * parameter can actually be the shard name or the HostAndPort for any
      * server in the shard.
      */
-    std::shared_ptr<Shard> getShard(OperationContext* txn, const ShardId& shardId);
+    StatusWith<std::shared_ptr<Shard>> getShard(OperationContext* txn, const ShardId& shardId);
 
     /**
      * Returns a shared pointer to the shard object with the given shard id. The shardId parameter
diff --git a/src/mongo/s/commands/cluster_add_shard_cmd.cpp b/src/mongo/s/commands/cluster_add_shard_cmd.cpp
index 40e861e6b6b..d6825da3c93 100644
--- a/src/mongo/s/commands/cluster_add_shard_cmd.cpp
+++ b/src/mongo/s/commands/cluster_add_shard_cmd.cpp
@@ -104,7 +104,7 @@ public:
 
         // Ensure the added shard is visible to this process.
         auto shardRegistry = Grid::get(txn)->shardRegistry();
-        if (!shardRegistry->getShard(txn, shardAdded)) {
+        if (!shardRegistry->getShard(txn, shardAdded).isOK()) {
             return appendCommandStatus(result,
                                        {ErrorCodes::OperationFailed,
                                         "Could not find shard metadata for shard after adding it. "
diff --git a/src/mongo/s/commands/cluster_explain.cpp b/src/mongo/s/commands/cluster_explain.cpp
index fa4b231741a..96b78d23f0a 100644
--- a/src/mongo/s/commands/cluster_explain.cpp
+++ b/src/mongo/s/commands/cluster_explain.cpp
@@ -220,7 +220,8 @@ void ClusterExplain::buildPlannerInfo(OperationContext* txn,
 
         singleShardBob.append("shardName", shardResults[i].shardTargetId.toString());
         {
-            const auto shard = grid.shardRegistry()->getShard(txn, shardResults[i].shardTargetId);
+            const auto shard =
+                uassertStatusOK(grid.shardRegistry()->getShard(txn, shardResults[i].shardTargetId));
             singleShardBob.append("connectionString", shard->getConnString().toString());
         }
         appendIfRoom(&singleShardBob, serverInfo, "serverInfo");
diff --git a/src/mongo/s/commands/cluster_find_and_modify_cmd.cpp b/src/mongo/s/commands/cluster_find_and_modify_cmd.cpp
index bea947aedda..73f1860118d 100644
--- a/src/mongo/s/commands/cluster_find_and_modify_cmd.cpp
+++ b/src/mongo/s/commands/cluster_find_and_modify_cmd.cpp
@@ -98,7 +98,11 @@ public:
         shared_ptr<Shard> shard;
 
         if (!conf->isShardingEnabled() || !conf->isSharded(nss.ns())) {
-            shard = Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+            auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+            if (!shardStatus.isOK()) {
+                return shardStatus.getStatus();
+            }
+            shard = shardStatus.getValue();
         } else {
             chunkMgr = _getChunkManager(txn, conf, nss);
 
@@ -128,7 +132,12 @@ public:
                           "to non-simple collation");
             }
 
-            shard = Grid::get(txn)->shardRegistry()->getShard(txn, chunk.getValue()->getShardId());
+            auto shardStatus =
+                Grid::get(txn)->shardRegistry()->getShard(txn, chunk.getValue()->getShardId());
+            if (!shardStatus.isOK()) {
+                return shardStatus.getStatus();
+            }
+            shard = shardStatus.getValue();
         }
 
         BSONObjBuilder explainCmd;
@@ -257,7 +266,8 @@ private:
                      BSONObjBuilder& result) const {
         BSONObj res;
 
-        const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+        const auto shard = uassertStatusOK(Grid::get(txn)->shardRegistry()->getShard(txn, shardId));
+
         ShardConnection conn(shard->getConnString(), nss.ns(), chunkManager);
         bool ok = conn->runCommand(conf->name(), cmdObj, res);
         conn.done();
diff --git a/src/mongo/s/commands/cluster_fsync_cmd.cpp b/src/mongo/s/commands/cluster_fsync_cmd.cpp
index 8a1ce646c2e..15e20e2c436 100644
--- a/src/mongo/s/commands/cluster_fsync_cmd.cpp
+++ b/src/mongo/s/commands/cluster_fsync_cmd.cpp
@@ -87,10 +87,11 @@ public:
         grid.shardRegistry()->getAllShardIds(&shardIds);
 
         for (const ShardId& shardId : shardIds) {
-            const auto s = grid.shardRegistry()->getShard(txn, shardId);
-            if (!s) {
+            auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
                 continue;
             }
+            const auto s = shardStatus.getValue();
 
             auto response =
                 uassertStatusOK(s->runCommand(txn,
diff --git a/src/mongo/s/commands/cluster_get_last_error_cmd.cpp b/src/mongo/s/commands/cluster_get_last_error_cmd.cpp
index 78d7e892391..56bfa66b369 100644
--- a/src/mongo/s/commands/cluster_get_last_error_cmd.cpp
+++ b/src/mongo/s/commands/cluster_get_last_error_cmd.cpp
@@ -111,13 +111,12 @@ public:
             const HostOpTime& hot = it->second;
 
             const ReadPreferenceSetting readPref(ReadPreference::PrimaryOnly, TagSet());
-            auto shard = grid.shardRegistry()->getShard(txn, shardEndpoint.toString());
-            if (!shard) {
-                status =
-                    Status(ErrorCodes::ShardNotFound,
-                           str::stream() << "shard " << shardEndpoint.toString() << " not found");
+            auto shardStatus = grid.shardRegistry()->getShard(txn, shardEndpoint.toString());
+            if (!shardStatus.isOK()) {
+                status = shardStatus.getStatus();
                 break;
             }
+            auto shard = shardStatus.getValue();
             auto swHostAndPort = shard->getTargeter()->findHost(readPref);
             if (!swHostAndPort.isOK()) {
                 status = swHostAndPort.getStatus();
diff --git a/src/mongo/s/commands/cluster_kill_op.cpp b/src/mongo/s/commands/cluster_kill_op.cpp
index ba698426fcc..bfbc556b36b 100644
--- a/src/mongo/s/commands/cluster_kill_op.cpp
+++ b/src/mongo/s/commands/cluster_kill_op.cpp
@@ -103,13 +103,11 @@ public:
         log() << "want to kill op: " << redact(opToKill);
 
         // Will throw if shard id is not found
-        auto shard = grid.shardRegistry()->getShard(txn, shardIdent);
-        if (!shard) {
-            return appendCommandStatus(
-                result,
-                Status(ErrorCodes::ShardNotFound,
-                       str::stream() << "shard " << shardIdent << " does not exist"));
+        auto shardStatus = grid.shardRegistry()->getShard(txn, shardIdent);
+        if (!shardStatus.isOK()) {
+            return appendCommandStatus(result, shardStatus.getStatus());
         }
+        auto shard = shardStatus.getValue();
 
         int opId;
         uassertStatusOK(parseNumberFromStringWithBase(opToKill.substr(opSepPos + 1), 10, &opId));
diff --git a/src/mongo/s/commands/cluster_list_databases_cmd.cpp b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
index 3b911f97588..7ea4cd7e8fc 100644
--- a/src/mongo/s/commands/cluster_list_databases_cmd.cpp
+++ b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
@@ -95,10 +95,11 @@ public:
         grid.shardRegistry()->getAllShardIds(&shardIds);
 
         for (const ShardId& shardId : shardIds) {
-            const auto s = grid.shardRegistry()->getShard(txn, shardId);
-            if (!s) {
+            const auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
                 continue;
             }
+            const auto s = shardStatus.getValue();
 
             auto response = uassertStatusOK(
                 s->runCommand(txn,
diff --git a/src/mongo/s/commands/cluster_map_reduce_cmd.cpp b/src/mongo/s/commands/cluster_map_reduce_cmd.cpp
index e398609c9e9..9978e6c142d 100644
--- a/src/mongo/s/commands/cluster_map_reduce_cmd.cpp
+++ b/src/mongo/s/commands/cluster_map_reduce_cmd.cpp
@@ -290,7 +290,9 @@ public:
         if (!shardedInput && !shardedOutput && !customOutDB) {
             LOG(1) << "simple MR, just passthrough";
 
-            const auto shard = grid.shardRegistry()->getShard(txn, confIn->getPrimaryId());
+            const auto shard =
+                uassertStatusOK(grid.shardRegistry()->getShard(txn, confIn->getPrimaryId()));
+
             ShardConnection conn(shard->getConnString(), "");
 
             BSONObj res;
@@ -348,7 +350,8 @@ public:
                 // Need to gather list of all servers even if an error happened
                 string server;
                 {
-                    const auto shard = grid.shardRegistry()->getShard(txn, mrResult.shardTargetId);
+                    const auto shard = uassertStatusOK(
+                        grid.shardRegistry()->getShard(txn, mrResult.shardTargetId));
                     server = shard->getConnString().toString();
                 }
                 servers.insert(server);
@@ -441,7 +444,9 @@ public:
         bool hasWCError = false;
 
         if (!shardedOutput) {
-            const auto shard = grid.shardRegistry()->getShard(txn, confOut->getPrimaryId());
+            const auto shard =
+                uassertStatusOK(grid.shardRegistry()->getShard(txn, confOut->getPrimaryId()));
+
             LOG(1) << "MR with single shard output, NS=" << outputCollNss.ns()
                    << " primary=" << shard->toString();
 
@@ -545,8 +550,8 @@ public:
                 for (const auto& mrResult : mrCommandResults) {
                     string server;
                     {
-                        const auto shard =
-                            grid.shardRegistry()->getShard(txn, mrResult.shardTargetId);
+                        const auto shard = uassertStatusOK(
+                            grid.shardRegistry()->getShard(txn, mrResult.shardTargetId));
                         server = shard->getConnString().toString();
                     }
                     singleResult = mrResult.result;
diff --git a/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp b/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
index d534c29aadd..44f8e74ccf2 100644
--- a/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
+++ b/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
@@ -185,15 +185,15 @@ public:
 
         // Throws, but handled at level above.  Don't want to rewrap to preserve exception
         // formatting.
-        const auto shard = grid.shardRegistry()->getShard(txn, firstChunk->getShardId());
-        if (!shard) {
+        const auto shardStatus = grid.shardRegistry()->getShard(txn, firstChunk->getShardId());
+        if (!shardStatus.isOK()) {
             return appendCommandStatus(
                 result,
                 Status(ErrorCodes::ShardNotFound,
                        str::stream() << "Can't find shard for chunk: " << firstChunk->toString()));
         }
 
-        ShardConnection conn(shard->getConnString(), "");
+        ShardConnection conn(shardStatus.getValue()->getConnString(), "");
         bool ok = conn->runCommand("admin", remoteCmdObjB.obj(), remoteResult);
         conn.done();
 
diff --git a/src/mongo/s/commands/cluster_move_chunk_cmd.cpp b/src/mongo/s/commands/cluster_move_chunk_cmd.cpp
index 282667dd6eb..4236beb6121 100644
--- a/src/mongo/s/commands/cluster_move_chunk_cmd.cpp
+++ b/src/mongo/s/commands/cluster_move_chunk_cmd.cpp
@@ -135,14 +135,15 @@ public:
             return false;
         }
 
-        const auto to = grid.shardRegistry()->getShard(txn, toString);
-        if (!to) {
+        const auto toStatus = grid.shardRegistry()->getShard(txn, toString);
+        if (!toStatus.isOK()) {
             string msg(str::stream() << "Could not move chunk in '" << nss.ns() << "' to shard '"
                                      << toString
                                      << "' because that shard does not exist");
             log() << msg;
             return appendCommandStatus(result, Status(ErrorCodes::ShardNotFound, msg));
         }
+        const auto to = toStatus.getValue();
 
         // so far, chunk size serves test purposes; it may or may not become a supported parameter
         long long maxChunkSizeBytes = cmdObj["maxChunkSizeBytes"].numberLong();
diff --git a/src/mongo/s/commands/cluster_move_primary_cmd.cpp b/src/mongo/s/commands/cluster_move_primary_cmd.cpp
index b4e6ce5e003..418ed3b25a0 100644
--- a/src/mongo/s/commands/cluster_move_primary_cmd.cpp
+++ b/src/mongo/s/commands/cluster_move_primary_cmd.cpp
@@ -130,17 +130,18 @@ public:
             return false;
         }
 
-        shared_ptr<Shard> toShard = grid.shardRegistry()->getShard(txn, to);
-        if (!toShard) {
+        auto toShardStatus = grid.shardRegistry()->getShard(txn, to);
+        if (!toShardStatus.isOK()) {
             string msg(str::stream() << "Could not move database '" << dbname << "' to shard '"
                                      << to
                                      << "' because the shard does not exist");
             log() << msg;
             return appendCommandStatus(result, Status(ErrorCodes::ShardNotFound, msg));
         }
+        auto toShard = toShardStatus.getValue();
 
-        shared_ptr<Shard> fromShard = grid.shardRegistry()->getShard(txn, config->getPrimaryId());
-        invariant(fromShard);
+        auto fromShard =
+            uassertStatusOK(grid.shardRegistry()->getShard(txn, config->getPrimaryId()));
 
         if (fromShard->getId() == toShard->getId()) {
             errmsg = "it is already the primary";
diff --git a/src/mongo/s/commands/cluster_pipeline_cmd.cpp b/src/mongo/s/commands/cluster_pipeline_cmd.cpp
index 8d14feaceec..19df5847a85 100644
--- a/src/mongo/s/commands/cluster_pipeline_cmd.cpp
+++ b/src/mongo/s/commands/cluster_pipeline_cmd.cpp
@@ -304,7 +304,9 @@ public:
         const auto& mergingShardId = needPrimaryShardMerger
             ? conf->getPrimaryId()
             : shardResults[prng.nextInt32(shardResults.size())].shardTargetId;
-        const auto mergingShard = grid.shardRegistry()->getShard(txn, mergingShardId);
+        const auto mergingShard =
+            uassertStatusOK(grid.shardRegistry()->getShard(txn, mergingShardId));
+
         ShardConnection conn(mergingShard->getConnString(), outputNsOrEmpty);
         BSONObj mergedResults =
             aggRunCommand(conn.get(), dbname, mergeCmd.freeze().toBson(), options);
@@ -490,15 +492,19 @@ bool PipelineCommand::aggPassthrough(OperationContext* txn,
                                      int queryOptions,
                                      std::string& errmsg) {
     // Temporary hack. See comment on declaration for details.
-    const auto shard = grid.shardRegistry()->getShard(txn, conf->getPrimaryId());
-    ShardConnection conn(shard->getConnString(), "");
+    auto shardStatus = grid.shardRegistry()->getShard(txn, conf->getPrimaryId());
+    if (!shardStatus.isOK()) {
+        return appendCommandStatus(out, shardStatus.getStatus());
+    }
+
+    ShardConnection conn(shardStatus.getValue()->getConnString(), "");
     BSONObj result = aggRunCommand(conn.get(), conf->name(), cmdObj, queryOptions);
     conn.done();
 
     // First append the properly constructed writeConcernError. It will then be skipped
     // in appendElementsUnique.
     if (auto wcErrorElem = result["writeConcernError"]) {
-        appendWriteConcernErrorToCmdResponse(shard->getId(), wcErrorElem, out);
+        appendWriteConcernErrorToCmdResponse(shardStatus.getValue()->getId(), wcErrorElem, out);
     }
 
     out.appendElementsUnique(result);
diff --git a/src/mongo/s/commands/cluster_remove_shard_cmd.cpp b/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
index 03dd30ae787..42acb26fd11 100644
--- a/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
+++ b/src/mongo/s/commands/cluster_remove_shard_cmd.cpp
@@ -87,13 +87,14 @@ public:
                      BSONObjBuilder& result) {
         const string target = cmdObj.firstElement().valuestrsafe();
 
-        const auto s = grid.shardRegistry()->getShard(txn, ShardId(target));
-        if (!s) {
+        const auto shardStatus = grid.shardRegistry()->getShard(txn, ShardId(target));
+        if (!shardStatus.isOK()) {
             string msg(str::stream() << "Could not drop shard '" << target
                                      << "' because it does not exist");
             log() << msg;
             return appendCommandStatus(result, Status(ErrorCodes::ShardNotFound, msg));
         }
+        const auto s = shardStatus.getValue();
 
         auto catalogClient = grid.catalogClient(txn);
         StatusWith<ShardDrainingStatus> removeShardResult =
diff --git a/src/mongo/s/commands/cluster_shard_collection_cmd.cpp b/src/mongo/s/commands/cluster_shard_collection_cmd.cpp
index 5471371e0e8..1f580f97493 100644
--- a/src/mongo/s/commands/cluster_shard_collection_cmd.cpp
+++ b/src/mongo/s/commands/cluster_shard_collection_cmd.cpp
@@ -206,7 +206,8 @@ public:
         // The rest of the checks require a connection to the primary db
         ConnectionString shardConnString;
         {
-            const auto shard = grid.shardRegistry()->getShard(txn, config->getPrimaryId());
+            const auto shard =
+                uassertStatusOK(grid.shardRegistry()->getShard(txn, config->getPrimaryId()));
             shardConnString = shard->getConnString();
         }
 
@@ -532,10 +533,11 @@ public:
             int i = 0;
             for (ChunkMap::const_iterator c = chunkMap.begin(); c != chunkMap.end(); ++c, ++i) {
                 const ShardId& shardId = shardIds[i % numShards];
-                const auto to = grid.shardRegistry()->getShard(txn, shardId);
-                if (!to) {
+                const auto toStatus = grid.shardRegistry()->getShard(txn, shardId);
+                if (!toStatus.isOK()) {
                     continue;
                 }
+                const auto to = toStatus.getValue();
 
                 shared_ptr<Chunk> chunk = c->second;
 
diff --git a/src/mongo/s/commands/cluster_user_management_commands.cpp b/src/mongo/s/commands/cluster_user_management_commands.cpp
index 28c750617d7..177855c50f1 100644
--- a/src/mongo/s/commands/cluster_user_management_commands.cpp
+++ b/src/mongo/s/commands/cluster_user_management_commands.cpp
@@ -854,16 +854,16 @@ Status runUpgradeOnAllShards(OperationContext* txn, int maxSteps, BSONObjBuilder
 
     bool hasWCError = false;
     for (const auto& shardId : shardIds) {
-        auto shard = shardRegistry->getShard(txn, shardId);
-        if (!shard) {
-            return {ErrorCodes::ShardNotFound,
-                    str::stream() << "shard " << shardId << " not found"};
+        auto shardStatus = shardRegistry->getShard(txn, shardId);
+        if (!shardStatus.isOK()) {
+            return shardStatus.getStatus();
         }
-        auto cmdResult = shard->runCommand(txn,
-                                           ReadPreferenceSetting{ReadPreference::PrimaryOnly},
-                                           "admin",
-                                           cmdObj,
-                                           Shard::RetryPolicy::kIdempotent);
+        auto cmdResult =
+            shardStatus.getValue()->runCommand(txn,
+                                               ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+                                               "admin",
+                                               cmdObj,
+                                               Shard::RetryPolicy::kIdempotent);
         auto status = cmdResult.isOK() ? std::move(cmdResult.getValue().commandStatus)
                                        : std::move(cmdResult.getStatus());
         if (!status.isOK()) {
diff --git a/src/mongo/s/commands/cluster_write_cmd.cpp b/src/mongo/s/commands/cluster_write_cmd.cpp
index 317019abb01..ea63a7d020a 100644
--- a/src/mongo/s/commands/cluster_write_cmd.cpp
+++ b/src/mongo/s/commands/cluster_write_cmd.cpp
@@ -267,12 +267,11 @@ private:
             const ShardEndpoint* endpoint = *it;
 
             const ReadPreferenceSetting readPref(ReadPreference::PrimaryOnly, TagSet());
-            auto shard = grid.shardRegistry()->getShard(txn, endpoint->shardName);
-            if (!shard) {
-                return Status(ErrorCodes::ShardNotFound,
-                              "Could not find shard with id " + endpoint->shardName.toString());
+            auto shardStatus = grid.shardRegistry()->getShard(txn, endpoint->shardName);
+            if (!shardStatus.isOK()) {
+                return shardStatus.getStatus();
             }
-            auto swHostAndPort = shard->getTargeter()->findHost(readPref);
+            auto swHostAndPort = shardStatus.getValue()->getTargeter()->findHost(readPref);
             if (!swHostAndPort.isOK()) {
                 return swHostAndPort.getStatus();
             }
@@ -300,8 +299,11 @@ private:
             Strategy::CommandResult result;
             result.target = host;
             {
-                const auto shard = grid.shardRegistry()->getShard(txn, host.toString());
-                result.shardTargetId = shard->getId();
+                auto shardStatus = grid.shardRegistry()->getShard(txn, host.toString());
+                if (!shardStatus.isOK()) {
+                    return shardStatus.getStatus();
+                }
+                result.shardTargetId = shardStatus.getValue()->getId();
             }
             result.result = response.toBSON();
 
diff --git a/src/mongo/s/commands/commands_public.cpp b/src/mongo/s/commands/commands_public.cpp
index 4610b4cca67..67d2ba99338 100644
--- a/src/mongo/s/commands/commands_public.cpp
+++ b/src/mongo/s/commands/commands_public.cpp
@@ -91,11 +91,12 @@ bool cursorCommandPassthrough(OperationContext* txn,
                               const BSONObj& cmdObj,
                               int options,
                               BSONObjBuilder* out) {
-    const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
-    if (!shard) {
-        return Command::appendCommandStatus(
-            *out, {ErrorCodes::ShardNotFound, "failed to find a valid shard"});
+    const auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+    if (!shardStatus.isOK()) {
+        invariant(shardStatus.getStatus() == ErrorCodes::ShardNotFound);
+        return Command::appendCommandStatus(*out, shardStatus.getStatus());
     }
+    const auto shard = shardStatus.getValue();
     ScopedDbConnection conn(shard->getConnString());
     auto cursor = conn->query(str::stream() << conf->name() << ".$cmd",
                               cmdObj,
@@ -198,7 +199,10 @@ private:
                       const BSONObj& cmdObj,
                       int options,
                       BSONObjBuilder& result) {
-        const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+        const auto shardStatus =
+            Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+        const auto shard = uassertStatusOK(shardStatus);
+
         ShardConnection conn(shard->getConnString(), "");
 
         BSONObj res;
@@ -673,8 +677,8 @@ public:
             }
 
             {
-                const auto& shard =
-                    Grid::get(txn)->shardRegistry()->getShard(txn, confFrom->getPrimaryId());
+                const auto shard = uassertStatusOK(
+                    Grid::get(txn)->shardRegistry()->getShard(txn, confFrom->getPrimaryId()));
                 b.append("fromhost", shard->getConnString().toString());
             }
             BSONObj fixed = b.obj();
@@ -732,10 +736,12 @@ public:
         set<ShardId> shardIds;
         cm->getAllShardIds(&shardIds);
         for (const ShardId& shardId : shardIds) {
-            const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-            if (!shard) {
+            const auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
+                invariant(shardStatus.getStatus() == ErrorCodes::ShardNotFound);
                 continue;
             }
+            const auto shard = shardStatus.getValue();
 
             BSONObj res;
             {
@@ -918,12 +924,13 @@ public:
         set<ShardId> shardIds;
         cm->getShardIdsForRange(shardIds, min, max);
         for (const ShardId& shardId : shardIds) {
-            const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-            if (!shard) {
+            const auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
+                invariant(shardStatus.getStatus() == ErrorCodes::ShardNotFound);
                 continue;
             }
 
-            ScopedDbConnection conn(shard->getConnString());
+            ScopedDbConnection conn(shardStatus.getValue()->getConnString());
             BSONObj res;
             bool ok = conn->runCommand(conf->name(), cmdObj, res);
             conn.done();
@@ -1028,12 +1035,15 @@ public:
                                         << ". Cannot run on sharded namespace.");
         }
 
-        const auto primaryShard =
+        const auto primaryShardStatus =
             Grid::get(txn)->shardRegistry()->getShard(txn, conf->getPrimaryId());
+        if (!primaryShardStatus.isOK()) {
+            return primaryShardStatus.getStatus();
+        }
 
         BSONObj shardResult;
         try {
-            ShardConnection conn(primaryShard->getConnString(), "");
+            ShardConnection conn(primaryShardStatus.getValue()->getConnString(), "");
 
             // TODO: this can throw a stale config when mongos is not up-to-date -- fix.
             if (!conn->runCommand(nss.db().toString(), command, shardResult, options)) {
@@ -1054,7 +1064,7 @@ public:
         Strategy::CommandResult cmdResult;
         cmdResult.shardTargetId = conf->getPrimaryId();
         cmdResult.result = shardResult;
-        cmdResult.target = primaryShard->getConnString();
+        cmdResult.target = primaryShardStatus.getValue()->getConnString();
 
         return ClusterExplain::buildExplainResult(
             txn, {cmdResult}, ClusterExplain::kSingleShard, timer.millis(), out);
@@ -1206,12 +1216,13 @@ public:
         BSONObjSet all = bsonCmp.makeBSONObjSet();
 
         for (const ShardId& shardId : shardIds) {
-            const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-            if (!shard) {
+            const auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
+                invariant(shardStatus.getStatus() == ErrorCodes::ShardNotFound);
                 continue;
             }
 
-            ShardConnection conn(shard->getConnString(), fullns);
+            ShardConnection conn(shardStatus.getValue()->getConnString(), fullns);
             BSONObj res;
             bool ok = conn->runCommand(conf->name(), cmdObj, res, options);
             conn.done();
@@ -1524,13 +1535,14 @@ public:
         list<shared_ptr<Future::CommandResult>> futures;
         BSONArrayBuilder shardArray;
         for (const ShardId& shardId : shardIds) {
-            const auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-            if (!shard) {
+            const auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+            if (!shardStatus.isOK()) {
+                invariant(shardStatus.getStatus() == ErrorCodes::ShardNotFound);
                 continue;
             }
 
-            futures.push_back(
-                Future::spawnCommand(shard->getConnString().toString(), dbName, cmdObj, options));
+            futures.push_back(Future::spawnCommand(
+                shardStatus.getValue()->getConnString().toString(), dbName, cmdObj, options));
             shardArray.append(shardId.toString());
         }
 
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 44858bb249f..9b0b26cf14b 100644
--- a/src/mongo/s/commands/run_on_all_shards_cmd.cpp
+++ b/src/mongo/s/commands/run_on_all_shards_cmd.cpp
@@ -88,13 +88,17 @@ bool RunOnAllShardsCommand::run(OperationContext* txn,
 
     std::list<std::shared_ptr<Future::CommandResult>> futures;
     for (const ShardId& shardId : shardIds) {
-        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
-        if (!shard) {
+        const auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+        if (!shardStatus.isOK()) {
             continue;
         }
 
-        futures.push_back(Future::spawnCommand(
-            shard->getConnString().toString(), dbName, cmdObj, 0, NULL, _useShardConn));
+        futures.push_back(Future::spawnCommand(shardStatus.getValue()->getConnString().toString(),
+                                               dbName,
+                                               cmdObj,
+                                               0,
+                                               NULL,
+                                               _useShardConn));
     }
 
     std::vector<ShardAndReply> results;
diff --git a/src/mongo/s/config.cpp b/src/mongo/s/config.cpp
index 6459d758beb..e830f9db187 100644
--- a/src/mongo/s/config.cpp
+++ b/src/mongo/s/config.cpp
@@ -225,7 +225,10 @@ void DBConfig::getChunkManagerOrPrimary(OperationContext* txn,
         // No namespace
         if (i == _collections.end()) {
             // If we don't know about this namespace, it's unsharded by default
-            primary = grid.shardRegistry()->getShard(txn, _primaryId);
+            auto primaryStatus = grid.shardRegistry()->getShard(txn, _primaryId);
+            if (primaryStatus.isOK()) {
+                primary = primaryStatus.getValue();
+            }
         } else {
             CollectionInfo& cInfo = i->second;
 
@@ -236,13 +239,16 @@ void DBConfig::getChunkManagerOrPrimary(OperationContext* txn,
             if (_shardingEnabled && cInfo.isSharded()) {
                 manager = cInfo.getCM();
             } else {
-                primary = grid.shardRegistry()->getShard(txn, _primaryId);
+                auto primaryStatus = grid.shardRegistry()->getShard(txn, _primaryId);
+                if (primaryStatus.isOK()) {
+                    primary = primaryStatus.getValue();
+                }
             }
         }
     }
 
-    verify(manager || primary);
-    verify(!manager || !primary);
+    invariant(manager || primary);
+    invariant(!manager || !primary);
 }
 
 
@@ -578,7 +584,8 @@ bool DBConfig::dropDatabase(OperationContext* txn, string& errmsg) {
 
     // 3
     {
-        const auto shard = grid.shardRegistry()->getShard(txn, _primaryId);
+        const auto shard = uassertStatusOK(grid.shardRegistry()->getShard(txn, _primaryId));
+
         ScopedDbConnection conn(shard->getConnString(), 30.0);
         BSONObj res;
         if (!conn->dropDatabase(_name, txn->getWriteConcern(), &res)) {
@@ -597,12 +604,12 @@ bool DBConfig::dropDatabase(OperationContext* txn, string& errmsg) {
 
     // 4
     for (const ShardId& shardId : shardIds) {
-        const auto shard = grid.shardRegistry()->getShard(txn, shardId);
-        if (!shard) {
+        const auto shardStatus = grid.shardRegistry()->getShard(txn, shardId);
+        if (!shardStatus.isOK()) {
             continue;
         }
 
-        ScopedDbConnection conn(shard->getConnString(), 30.0);
+        ScopedDbConnection conn(shardStatus.getValue()->getConnString(), 30.0);
         BSONObj res;
         if (!conn->dropDatabase(_name, txn->getWriteConcern(), &res)) {
             errmsg = res.toString() + " at " + shardId.toString();
diff --git a/src/mongo/s/query/cluster_find.cpp b/src/mongo/s/query/cluster_find.cpp
index 7d8b12260a7..0ad02215ed2 100644
--- a/src/mongo/s/query/cluster_find.cpp
+++ b/src/mongo/s/query/cluster_find.cpp
@@ -168,12 +168,11 @@ StatusWith<CursorId> runQueryWithoutRetrying(OperationContext* txn,
                                           &shardIds);
 
         for (auto id : shardIds) {
-            auto shard = shardRegistry->getShard(txn, id);
-            if (!shard) {
-                return {ErrorCodes::ShardNotFound,
-                        str::stream() << "Shard with id:  " << id << " is not found."};
+            auto shardStatus = shardRegistry->getShard(txn, id);
+            if (!shardStatus.isOK()) {
+                return shardStatus.getStatus();
             }
-            shards.emplace_back(shard);
+            shards.emplace_back(shardStatus.getValue());
         }
     }
 
diff --git a/src/mongo/s/shard_util.cpp b/src/mongo/s/shard_util.cpp
index 8e690c93188..4b1b2b2fb51 100644
--- a/src/mongo/s/shard_util.cpp
+++ b/src/mongo/s/shard_util.cpp
@@ -55,17 +55,17 @@ const char kShouldMigrate[] = "shouldMigrate";
 }  // namespace
 
 StatusWith<long long> retrieveTotalShardSize(OperationContext* txn, const ShardId& shardId) {
-    auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-    if (!shard) {
-        return Status(ErrorCodes::ShardNotFound,
-                      str::stream() << "shard " << shardId << " not found");
+    auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+    if (!shardStatus.isOK()) {
+        return shardStatus.getStatus();
     }
+
     auto listDatabasesStatus =
-        shard->runCommand(txn,
-                          ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
-                          "admin",
-                          BSON("listDatabases" << 1),
-                          Shard::RetryPolicy::kIdempotent);
+        shardStatus.getValue()->runCommand(txn,
+                                           ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
+                                           "admin",
+                                           BSON("listDatabases" << 1),
+                                           Shard::RetryPolicy::kIdempotent);
     if (!listDatabasesStatus.isOK()) {
         return std::move(listDatabasesStatus.getStatus());
     }
@@ -94,16 +94,17 @@ StatusWith<BSONObj> selectMedianKey(OperationContext* txn,
     cmd.append(kMaxKey, maxKey);
     cmd.appendBool("force", true);
 
-    auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-    if (!shard) {
-        return Status(ErrorCodes::ShardNotFound,
-                      str::stream() << "shard " << shardId << " not found");
+    auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+    if (!shardStatus.isOK()) {
+        return shardStatus.getStatus();
     }
-    auto cmdStatus = shard->runCommand(txn,
-                                       ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
-                                       "admin",
-                                       cmd.obj(),
-                                       Shard::RetryPolicy::kIdempotent);
+
+    auto cmdStatus =
+        shardStatus.getValue()->runCommand(txn,
+                                           ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
+                                           "admin",
+                                           cmd.obj(),
+                                           Shard::RetryPolicy::kIdempotent);
     if (!cmdStatus.isOK()) {
         return std::move(cmdStatus.getStatus());
     }
@@ -139,16 +140,17 @@ StatusWith<std::vector<BSONObj>> selectChunkSplitPoints(OperationContext* txn,
     cmd.append("maxSplitPoints", maxPoints);
     cmd.append("maxChunkObjects", maxObjs);
 
-    auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-    if (!shard) {
-        return Status(ErrorCodes::ShardNotFound,
-                      str::stream() << "shard " << shardId << " not found");
+    auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+    if (!shardStatus.isOK()) {
+        return shardStatus.getStatus();
     }
-    auto cmdStatus = shard->runCommand(txn,
-                                       ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
-                                       "admin",
-                                       cmd.obj(),
-                                       Shard::RetryPolicy::kIdempotent);
+
+    auto cmdStatus =
+        shardStatus.getValue()->runCommand(txn,
+                                           ReadPreferenceSetting{ReadPreference::PrimaryPreferred},
+                                           "admin",
+                                           cmd.obj(),
+                                           Shard::RetryPolicy::kIdempotent);
     if (!cmdStatus.isOK()) {
         return std::move(cmdStatus.getStatus());
     }
@@ -206,16 +208,16 @@ StatusWith<boost::optional<ChunkRange>> splitChunkAtMultiplePoints(
     Status status{ErrorCodes::InternalError, "Uninitialized value"};
     BSONObj cmdResponse;
 
-    auto shard = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
-    if (!shard) {
-        status =
-            Status(ErrorCodes::ShardNotFound, str::stream() << "shard " << shardId << " not found");
+    auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(txn, shardId);
+    if (!shardStatus.isOK()) {
+        status = shardStatus.getStatus();
     } else {
-        auto cmdStatus = shard->runCommand(txn,
-                                           ReadPreferenceSetting{ReadPreference::PrimaryOnly},
-                                           "admin",
-                                           cmdObj,
-                                           Shard::RetryPolicy::kNotIdempotent);
+        auto cmdStatus =
+            shardStatus.getValue()->runCommand(txn,
+                                               ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+                                               "admin",
+                                               cmdObj,
+                                               Shard::RetryPolicy::kNotIdempotent);
         if (!cmdStatus.isOK()) {
             status = std::move(cmdStatus.getStatus());
         } else {
diff --git a/src/mongo/s/write_ops/batch_write_exec.cpp b/src/mongo/s/write_ops/batch_write_exec.cpp
index 1c1b0869933..34f399267f4 100644
--- a/src/mongo/s/write_ops/batch_write_exec.cpp
+++ b/src/mongo/s/write_ops/batch_write_exec.cpp
@@ -170,16 +170,14 @@ void BatchWriteExec::executeBatch(OperationContext* txn,
                     continue;
 
                 // Figure out what host we need to dispatch our targeted batch
-                bool resolvedHost = true;
                 const ReadPreferenceSetting readPref(ReadPreference::PrimaryOnly, TagSet());
-                auto shard = Grid::get(txn)->shardRegistry()->getShard(
+                auto shardStatus = Grid::get(txn)->shardRegistry()->getShard(
                     txn, nextBatch->getEndpoint().shardName);
 
-                if (!shard) {
-                    Status status = Status(ErrorCodes::ShardNotFound,
-                                           str::stream() << "unknown shard name "
-                                                         << nextBatch->getEndpoint().shardName);
-                    resolvedHost = false;
+                bool resolvedHost = false;
+                ConnectionString shardHost;
+                if (!shardStatus.isOK()) {
+                    Status status(std::move(shardStatus.getStatus()));
 
                     // Record a resolve failure
                     // TODO: It may be necessary to refresh the cache if stale, or maybe just
@@ -189,20 +187,25 @@ void BatchWriteExec::executeBatch(OperationContext* txn,
                     LOG(4) << "unable to send write batch to " << nextBatch->getEndpoint().shardName
                            << causedBy(status);
                     batchOp.noteBatchError(*nextBatch, error);
-                }
-
-                auto swHostAndPort = shard->getTargeter()->findHost(readPref);
-                if (!swHostAndPort.isOK()) {
-                    resolvedHost = false;
-
-                    // Record a resolve failure
-                    // TODO: It may be necessary to refresh the cache if stale, or maybe just
-                    // cancel and retarget the batch
-                    WriteErrorDetail error;
-                    buildErrorFrom(swHostAndPort.getStatus(), &error);
-                    LOG(4) << "unable to send write batch to " << nextBatch->getEndpoint().shardName
-                           << causedBy(swHostAndPort.getStatus());
-                    batchOp.noteBatchError(*nextBatch, error);
+                } else {
+                    auto shard = shardStatus.getValue();
+
+                    auto swHostAndPort = shard->getTargeter()->findHost(readPref);
+                    if (!swHostAndPort.isOK()) {
+
+                        // Record a resolve failure
+                        // TODO: It may be necessary to refresh the cache if stale, or maybe just
+                        // cancel and retarget the batch
+                        WriteErrorDetail error;
+                        buildErrorFrom(swHostAndPort.getStatus(), &error);
+                        LOG(4) << "unable to send write batch to "
+                               << nextBatch->getEndpoint().shardName
+                               << causedBy(swHostAndPort.getStatus());
+                        batchOp.noteBatchError(*nextBatch, error);
+                    } else {
+                        shardHost = ConnectionString(std::move(swHostAndPort.getValue()));
+                        resolvedHost = true;
+                    }
                 }
 
                 if (!resolvedHost) {
@@ -216,8 +219,6 @@ void BatchWriteExec::executeBatch(OperationContext* txn,
                     continue;
                 }
 
-                ConnectionString shardHost(swHostAndPort.getValue());
-
                 // If we already have a batch for this host, wait until the next time
                 OwnedHostBatchMap::MapType::iterator pendingIt = pendingBatches.find(shardHost);
                 if (pendingIt != pendingBatches.end())