SERVER-35486 Create _addShard command on shard to drive shard initialization

22 files changed, 534 insertions, 322 deletions

diff --git a/jstests/auth/lib/commands_lib.js b/jstests/auth/lib/commands_lib.js
index 5d057a65c2e..9a9b724e015 100644
--- a/jstests/auth/lib/commands_lib.js
+++ b/jstests/auth/lib/commands_lib.js
@@ -202,6 +202,28 @@ var authCommandsLib = {
           ]
         },
         {
+          testname: "_addShard",
+          command: {
+              _addShard: 1,
+              shardIdentity: {
+                  shardName: "shard0000",
+                  clusterId: ObjectId('5b2031806195dffd744258ee'),
+                  configsvrConnectionString: "foobarbaz/host:20022,host:20023,host:20024"
+              }
+          },
+          skipSharded: true,  // Command doesn't exist on mongos
+          testcases: [
+              {
+                runOnDb: adminDbName,
+                roles: {__system: 1},
+                privileges: [{resource: {cluster: true}, actions: ["internal"]}],
+                expectFail: true
+              },
+              {runOnDb: firstDbName, roles: {}},
+              {runOnDb: secondDbName, roles: {}}
+          ]
+        },
+        {
           testname: "addShard",
           command: {addShard: "x"},
           skipUnlessSharded: true,
diff --git a/jstests/core/views/views_all_commands.js b/jstests/core/views/views_all_commands.js
index a3b175f5b3a..de5c5dd1676 100644
--- a/jstests/core/views/views_all_commands.js
+++ b/jstests/core/views/views_all_commands.js
@@ -66,6 +66,7 @@
     const isUnrelated = "is unrelated";
 
     let viewsCommandTests = {
+        _addShard: {skip: isAnInternalCommand},
         _cloneCatalogData: {skip: isAnInternalCommand},
         _configsvrAddShard: {skip: isAnInternalCommand},
         _configsvrAddShardToZone: {skip: isAnInternalCommand},
diff --git a/jstests/sharding/safe_secondary_reads_drop_recreate.js b/jstests/sharding/safe_secondary_reads_drop_recreate.js
index b687586816b..d8f4f7fe8d2 100644
--- a/jstests/sharding/safe_secondary_reads_drop_recreate.js
+++ b/jstests/sharding/safe_secondary_reads_drop_recreate.js
@@ -36,6 +36,7 @@
     };
 
     let testCases = {
+        _addShard: {skip: "primary only"},
         _cloneCatalogData: {skip: "primary only"},
         _configsvrAddShard: {skip: "primary only"},
         _configsvrAddShardToZone: {skip: "primary only"},
diff --git a/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js b/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
index e51585e26c0..13605561e74 100644
--- a/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
+++ b/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
@@ -43,6 +43,7 @@
     };
 
     let testCases = {
+        _addShard: {skip: "primary only"},
         _cloneCatalogData: {skip: "primary only"},
         _configsvrAddShard: {skip: "primary only"},
         _configsvrAddShardToZone: {skip: "primary only"},
diff --git a/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js b/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
index 9611135a6ac..85f236dbae1 100644
--- a/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
+++ b/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
@@ -36,6 +36,7 @@
     };
 
     let testCases = {
+        _addShard: {skip: "primary only"},
         _cloneCatalogData: {skip: "primary only"},
         _configsvrAddShard: {skip: "primary only"},
         _configsvrAddShardToZone: {skip: "primary only"},
diff --git a/src/mongo/client/connection_string.cpp b/src/mongo/client/connection_string.cpp
index 5e8a5f4e0bb..b4d4eed0a00 100644
--- a/src/mongo/client/connection_string.cpp
+++ b/src/mongo/client/connection_string.cpp
@@ -217,6 +217,10 @@ StatusWith<ConnectionString> ConnectionString::parse(const std::string& url) {
     return Status(ErrorCodes::FailedToParse, str::stream() << "invalid url [" << url << "]");
 }
 
+ConnectionString ConnectionString::deserialize(StringData url) {
+    return uassertStatusOK(parse(url.toString()));
+}
+
 std::string ConnectionString::typeToString(ConnectionType type) {
     switch (type) {
         case INVALID:
diff --git a/src/mongo/client/connection_string.h b/src/mongo/client/connection_string.h
index 0467a77dce3..3c8a327a781 100644
--- a/src/mongo/client/connection_string.h
+++ b/src/mongo/client/connection_string.h
@@ -127,6 +127,12 @@ public:
 
     static StatusWith<ConnectionString> parse(const std::string& url);
 
+    /**
+     * Deserialize a ConnectionString object from a string. Used by the IDL parser for the
+     * connectionstring type. Essentially just a throwing wrapper around ConnectionString::parse.
+     */
+    static ConnectionString deserialize(StringData url);
+
     static std::string typeToString(ConnectionType type);
 
     //
diff --git a/src/mongo/db/s/SConscript b/src/mongo/db/s/SConscript
index 2216e68abae..cb57c8b8456 100644
--- a/src/mongo/db/s/SConscript
+++ b/src/mongo/db/s/SConscript
@@ -95,6 +95,7 @@ env.Library(
 env.Library(
     target='type_shard_identity',
     source=[
+        env.Idlc('add_shard_cmd.idl')[0],
         'type_shard_identity.cpp',
     ],
     LIBDEPS=[
@@ -184,6 +185,7 @@ env.CppUnitTest(
 env.Library(
     target='sharding_catalog_manager',
     source=[
+        'add_shard_util.cpp',
         'config/sharding_catalog_manager_chunk_operations.cpp',
         'config/sharding_catalog_manager_collection_operations.cpp',
         'config/sharding_catalog_manager.cpp',
@@ -214,6 +216,7 @@ env.Library(
 env.Library(
     target='commands_db_s',
     source=[
+        'add_shard_cmd.cpp',
         'check_sharding_index_command.cpp',
         'cleanup_orphaned_cmd.cpp',
         'clone_catalog_data_command.cpp',
diff --git a/src/mongo/db/s/add_shard_cmd.cpp b/src/mongo/db/s/add_shard_cmd.cpp
new file mode 100644
index 00000000000..0f06a488cd8
--- /dev/null
+++ b/src/mongo/db/s/add_shard_cmd.cpp
@@ -0,0 +1,103 @@
+/**
+ *    Copyright (C) 2018 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 "mongo/db/audit.h"
+#include "mongo/db/auth/action_type.h"
+#include "mongo/db/auth/authorization_session.h"
+#include "mongo/db/auth/privilege.h"
+#include "mongo/db/commands.h"
+#include "mongo/db/dbdirectclient.h"
+#include "mongo/db/s/add_shard_cmd_gen.h"
+#include "mongo/db/s/add_shard_util.h"
+#include "mongo/db/s/config/sharding_catalog_manager.h"
+#include "mongo/rpc/get_status_from_command_result.h"
+#include "mongo/util/log.h"
+
+namespace mongo {
+namespace {
+/**
+ * Internal sharding command run on mongod to initialize itself as a shard in the cluster.
+ */
+class AddShardCommand : public TypedCommand<AddShardCommand> {
+public:
+    using Request = AddShard;
+    class Invocation final : public InvocationBase {
+    public:
+        using InvocationBase::InvocationBase;
+
+        void typedRun(OperationContext* opCtx) {
+            auto addShardCmd = request();
+            auto shardIdUpsertCmd =
+                add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+            DBDirectClient localClient(opCtx);
+            BSONObj res;
+
+            localClient.runCommand(NamespaceString::kAdminDb.toString(), shardIdUpsertCmd, res);
+            uassertStatusOK(getStatusFromCommandResult(res));
+        }
+
+    private:
+        bool supportsWriteConcern() const override {
+            return true;
+        }
+
+        // The command parameter happens to be string so it's historically been interpreted
+        // by parseNs as a collection. Continuing to do so here for unexamined compatibility.
+        NamespaceString ns() const override {
+            return NamespaceString(request().getDbName(), "");
+        }
+
+        void doCheckAuthorization(OperationContext* opCtx) const override {
+            uassert(ErrorCodes::Unauthorized,
+                    "Unauthorized",
+                    AuthorizationSession::get(opCtx->getClient())
+                        ->isAuthorizedForActionsOnResource(ResourcePattern::forClusterResource(),
+                                                           ActionType::internal));
+        }
+    };
+
+    std::string help() const override {
+        return "Internal command, which is exported by shards. Do not call "
+               "directly. Adds a new shard to a cluster.";
+    }
+
+    AllowedOnSecondary secondaryAllowed(ServiceContext*) const override {
+        return AllowedOnSecondary::kNever;
+    }
+
+    bool adminOnly() const override {
+        return true;
+    }
+} addShardCmd;
+
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/db/s/add_shard_cmd.idl b/src/mongo/db/s/add_shard_cmd.idl
new file mode 100644
index 00000000000..fe6af62c7e2
--- /dev/null
+++ b/src/mongo/db/s/add_shard_cmd.idl
@@ -0,0 +1,53 @@
+# Copyright (C) 2018 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/>.
+#
+global:
+    cpp_namespace: "mongo"
+    cpp_includes:
+        - "mongo/client/connection_string.h"
+
+imports:
+    - "mongo/idl/basic_types.idl"
+
+types:
+    connectionstring:
+        bson_serialization_type: string
+        description: "A MongoDB ConnectionString"
+        cpp_type: "mongo::ConnectionString"
+        serializer: mongo::ConnectionString::toString
+        deserializer: mongo::ConnectionString::deserialize
+
+structs:
+    ShardIdentity:
+        description: "Contains all the information needed to identify a shard and lookup the shard identity document from storage"
+        fields:
+            shardName:
+                description: "The name of the shard"
+                type: string
+            clusterId:
+                description: "The unique identifier of the cluster"
+                type: objectid
+            configsvrConnectionString:
+                description: "Connection string to the config server"
+                type: connectionstring
+
+commands:
+    _addShard:
+        cpp_name: AddShard
+        description: "_addShard Command"
+        namespace: ignored
+        fields:
+            shardIdentity:
+                description: "Identity metadata for the new shard"
+                type: ShardIdentity
diff --git a/src/mongo/db/s/add_shard_util.cpp b/src/mongo/db/s/add_shard_util.cpp
new file mode 100644
index 00000000000..a71016243b8
--- /dev/null
+++ b/src/mongo/db/s/add_shard_util.cpp
@@ -0,0 +1,80 @@
+/**
+ * Copyright (C) 2018 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/platform/basic.h"
+
+#include "mongo/db/s/add_shard_util.h"
+
+#include "mongo/bson/bsonobj.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/ops/write_ops.h"
+#include "mongo/db/repl/repl_set_config.h"
+#include "mongo/db/repl/replication_coordinator.h"
+#include "mongo/db/s/add_shard_cmd_gen.h"
+#include "mongo/s/catalog/sharding_catalog_client.h"
+#include "mongo/s/cluster_identity_loader.h"
+#include "mongo/s/shard_id.h"
+#include "mongo/s/write_ops/batched_command_request.h"
+
+namespace mongo {
+namespace add_shard_util {
+
+AddShard createAddShardCmd(OperationContext* opCtx, const ShardId& shardName) {
+    AddShard addShardCmd;
+    addShardCmd.setDbName(NamespaceString::kAdminDb);
+
+    ShardIdentity shardIdentity;
+    shardIdentity.setShardName(shardName.toString());
+    shardIdentity.setClusterId(ClusterIdentityLoader::get(opCtx)->getClusterId());
+    shardIdentity.setConfigsvrConnectionString(
+        repl::ReplicationCoordinator::get(opCtx)->getConfig().getConnectionString());
+
+    addShardCmd.setShardIdentity(shardIdentity);
+    return addShardCmd;
+}
+
+BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd) {
+    BatchedCommandRequest request([&] {
+        write_ops::Update updateOp(NamespaceString::kServerConfigurationNamespace);
+        updateOp.setUpdates({[&] {
+            write_ops::UpdateOpEntry entry;
+            entry.setQ(BSON("_id" << kShardIdentityDocumentId));
+            entry.setU(addShardCmd.getShardIdentity().toBSON());
+            entry.setUpsert(true);
+            return entry;
+        }()});
+
+        return updateOp;
+    }());
+    request.setWriteConcern(ShardingCatalogClient::kMajorityWriteConcern.toBSON());
+
+    return request.toBSON();
+}
+
+}  // namespace mongo
+}  // namespace add_shard_util
diff --git a/src/mongo/db/s/add_shard_util.h b/src/mongo/db/s/add_shard_util.h
new file mode 100644
index 00000000000..9a525e44a58
--- /dev/null
+++ b/src/mongo/db/s/add_shard_util.h
@@ -0,0 +1,63 @@
+/**
+ * Copyright (C) 2018 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 <string>
+
+#include "mongo/base/string_data.h"
+
+namespace mongo {
+class AddShard;
+class BSONObj;
+class OperationContext;
+class ShardId;
+
+// Contains a collection of utility functions relating to the addShard command
+namespace add_shard_util {
+
+/*
+ * The _id value for shard identity documents
+ */
+constexpr StringData kShardIdentityDocumentId = "shardIdentity"_sd;
+
+/**
+ * Creates an AddShard command object that's sent from the config server to
+ * a mongod to instruct it to initialize itself as a shard in the cluster.
+ */
+AddShard createAddShardCmd(OperationContext* opCtx, const ShardId& shardName);
+
+/**
+ * Returns a BSON representation of an update request that can be used to insert a shardIdentity
+ * doc into the shard with the given shardName (or update the shard's existing shardIdentity
+ * doc's configsvrConnString if the _id, shardName, and clusterId do not conflict).
+ */
+BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd);
+
+}  // namespace mongo
+}  // namespace add_shard_util
diff --git a/src/mongo/db/s/collection_sharding_state_test.cpp b/src/mongo/db/s/collection_sharding_state_test.cpp
index d416840861c..401edadd7a0 100644
--- a/src/mongo/db/s/collection_sharding_state_test.cpp
+++ b/src/mongo/db/s/collection_sharding_state_test.cpp
@@ -66,19 +66,19 @@ private:
 
 TEST_F(CollectionShardingStateTest, GlobalInitGetsCalledAfterWriteCommits) {
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName("a");
     shardIdentity.setClusterId(OID::gen());
 
     DBDirectClient client(operationContext());
-    client.insert("admin.system.version", shardIdentity.toBSON());
+    client.insert("admin.system.version", shardIdentity.toShardIdentityDocument());
     ASSERT_EQ(1, getInitCallCount());
 }
 
 TEST_F(CollectionShardingStateTest, GlobalInitDoesntGetCalledIfWriteAborts) {
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName("a");
     shardIdentity.setClusterId(OID::gen());
@@ -95,7 +95,7 @@ TEST_F(CollectionShardingStateTest, GlobalInitDoesntGetCalledIfWriteAborts) {
 
         WriteUnitOfWork wuow(operationContext());
         ASSERT_OK(autoColl.getCollection()->insertDocument(
-            operationContext(), shardIdentity.toBSON(), {}, false));
+            operationContext(), shardIdentity.toShardIdentityDocument(), {}, false));
         ASSERT_EQ(0, getInitCallCount());
     }
 
@@ -104,22 +104,21 @@ TEST_F(CollectionShardingStateTest, GlobalInitDoesntGetCalledIfWriteAborts) {
 
 TEST_F(CollectionShardingStateTest, GlobalInitDoesntGetsCalledIfNSIsNotForShardIdentity) {
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName("a");
     shardIdentity.setClusterId(OID::gen());
 
     DBDirectClient client(operationContext());
-    client.insert("admin.user", shardIdentity.toBSON());
+    client.insert("admin.user", shardIdentity.toShardIdentityDocument());
     ASSERT_EQ(0, getInitCallCount());
 }
 
 TEST_F(CollectionShardingStateTest, OnInsertOpThrowWithIncompleteShardIdentityDocument) {
-    ShardIdentityType shardIdentity;
-    shardIdentity.setShardName("a");
-
     DBDirectClient client(operationContext());
-    client.insert("admin.system.version", shardIdentity.toBSON());
+    client.insert(
+        "admin.system.version",
+        BSON("_id" << ShardIdentityType::IdName << ShardIdentity::kShardNameFieldName << "a"));
     ASSERT(!client.getLastError().empty());
 }
 
diff --git a/src/mongo/db/s/config/sharding_catalog_manager.h b/src/mongo/db/s/config/sharding_catalog_manager.h
index 15edcbd1319..77938d09d82 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager.h
+++ b/src/mongo/db/s/config/sharding_catalog_manager.h
@@ -342,14 +342,6 @@ public:
     //
 
     /**
-     * Returns a BSON representation of an update request that can be used to insert a shardIdentity
-     * doc into the shard for the given shardType (or update the shard's existing shardIdentity
-     * doc's configsvrConnString if the _id, shardName, and clusterId do not conflict).
-     */
-    BSONObj createShardIdentityUpsertForAddShard(OperationContext* opCtx,
-                                                 const std::string& shardName);
-
-    /**
      * Runs the setFeatureCompatibilityVersion command on all shards.
      */
     Status setFeatureCompatibilityVersionOnShards(OperationContext* opCtx, const BSONObj& cmdObj);
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
index 1ec6b87f2cc..60bb75312d0 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
@@ -38,6 +38,8 @@
 #include "mongo/db/commands.h"
 #include "mongo/db/ops/write_ops.h"
 #include "mongo/db/repl/replication_coordinator_mock.h"
+#include "mongo/db/s/add_shard_cmd_gen.h"
+#include "mongo/db/s/add_shard_util.h"
 #include "mongo/db/s/config/sharding_catalog_manager.h"
 #include "mongo/db/s/type_shard_identity.h"
 #include "mongo/s/catalog/config_server_version.h"
@@ -153,12 +155,12 @@ protected:
      * Waits for a request for the shardIdentity document to be upserted into a shard from the
      * config server on addShard.
      */
-    void expectShardIdentityUpsertReturnSuccess(const HostAndPort& expectedHost,
-                                                const std::string& expectedShardName) {
+    void expectAddShardCmdReturnSuccess(const HostAndPort& expectedHost,
+                                        const std::string& expectedShardName) {
+        using namespace add_shard_util;
         // Create the expected upsert shardIdentity command for this shardType.
-        auto upsertCmdObj =
-            ShardingCatalogManager::get(operationContext())
-                ->createShardIdentityUpsertForAddShard(operationContext(), expectedShardName);
+        auto upsertCmdObj = createShardIdentityUpsertForAddShard(
+            createAddShardCmd(operationContext(), expectedShardName));
 
         const auto opMsgRequest =
             OpMsgRequest::fromDBAndBody(NamespaceString::kAdminDb, upsertCmdObj);
@@ -167,13 +169,13 @@ protected:
                                    UpdateOp::parse(opMsgRequest));
     }
 
-    void expectShardIdentityUpsertReturnFailure(const HostAndPort& expectedHost,
-                                                const std::string& expectedShardName,
-                                                const Status& statusToReturn) {
+    void expectAddShardCmdReturnFailure(const HostAndPort& expectedHost,
+                                        const std::string& expectedShardName,
+                                        const Status& statusToReturn) {
+        using namespace add_shard_util;
         // Create the expected upsert shardIdentity command for this shardType.
-        auto upsertCmdObj =
-            ShardingCatalogManager::get(operationContext())
-                ->createShardIdentityUpsertForAddShard(operationContext(), expectedShardName);
+        auto upsertCmdObj = createShardIdentityUpsertForAddShard(
+            createAddShardCmd(operationContext(), expectedShardName));
 
         const auto opMsgRequest =
             OpMsgRequest::fromDBAndBody(NamespaceString::kAdminDb, upsertCmdObj);
@@ -196,8 +198,20 @@ protected:
             // Check that the db name in the request matches the expected db name.
             ASSERT_EQUALS(expectedNss.db(), request.dbname);
 
-            const auto opMsgRequest = OpMsgRequest::fromDBAndBody(request.dbname, request.cmdObj);
-            const auto updateOp = UpdateOp::parse(opMsgRequest);
+            const auto addShardOpMsgRequest =
+                OpMsgRequest::fromDBAndBody(request.dbname, request.cmdObj);
+
+            auto addShardCmd = AddShard::parse(IDLParserErrorContext(AddShard::kCommandName),
+                                               addShardOpMsgRequest);
+
+            const auto& updateOpField =
+                add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+
+            const auto updateOpMsgRequest =
+                OpMsgRequest::fromDBAndBody(request.dbname, updateOpField);
+
+            const auto updateOp = UpdateOp::parse(updateOpMsgRequest);
+
             ASSERT_EQUALS(expectedNss, expectedUpdateOp.getNamespace());
 
             const auto& expectedUpdates = expectedUpdateOp.getUpdates();
@@ -336,23 +350,21 @@ TEST_F(AddShardTest, CreateShardIdentityUpsertForAddShard) {
                                 << "ordered"
                                 << true
                                 << "updates"
-                                << BSON_ARRAY(
-                                       BSON("q" << BSON("_id"
-                                                        << "shardIdentity"
-                                                        << "shardName"
-                                                        << shardName
-                                                        << "clusterId"
-                                                        << _clusterId)
-                                                << "u"
-                                                << BSON("$set" << BSON("configsvrConnectionString"
-                                                                       << replicationCoordinator()
-                                                                              ->getConfig()
-                                                                              .getConnectionString()
-                                                                              .toString()))
-                                                << "multi"
-                                                << false
-                                                << "upsert"
-                                                << true))
+                                << BSON_ARRAY(BSON(
+                                       "q"
+                                       << BSON("_id"
+                                               << "shardIdentity")
+                                       << "u"
+                                       << BSON("shardName" << shardName << "clusterId" << _clusterId
+                                                           << "configsvrConnectionString"
+                                                           << replicationCoordinator()
+                                                                  ->getConfig()
+                                                                  .getConnectionString()
+                                                                  .toString())
+                                       << "multi"
+                                       << false
+                                       << "upsert"
+                                       << true))
                                 << "writeConcern"
                                 << BSON("w"
                                         << "majority"
@@ -360,9 +372,9 @@ TEST_F(AddShardTest, CreateShardIdentityUpsertForAddShard) {
                                         << 15000)
                                 << "allowImplicitCollectionCreation"
                                 << true);
-    ASSERT_BSONOBJ_EQ(expectedBSON,
-                      ShardingCatalogManager::get(operationContext())
-                          ->createShardIdentityUpsertForAddShard(operationContext(), shardName));
+    auto addShardCmd = add_shard_util::createAddShardCmd(operationContext(), shardName);
+    auto actualBSON = add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+    ASSERT_BSONOBJ_EQ(expectedBSON, actualBSON);
 }
 
 TEST_F(AddShardTest, StandaloneBasicSuccess) {
@@ -416,8 +428,8 @@ TEST_F(AddShardTest, StandaloneBasicSuccess) {
 
     expectCollectionDrop(shardTarget, NamespaceString("config", "system.sessions"));
 
-    // The shardIdentity doc inserted into the admin.system.version collection on the shard.
-    expectShardIdentityUpsertReturnSuccess(shardTarget, expectedShardName);
+    // The shard receives the _addShard command
+    expectAddShardCmdReturnSuccess(shardTarget, expectedShardName);
 
     // The shard receives the setFeatureCompatibilityVersion command.
     expectSetFeatureCompatibilityVersion(
@@ -495,8 +507,8 @@ TEST_F(AddShardTest, StandaloneGenerateName) {
 
     expectCollectionDrop(shardTarget, NamespaceString("config", "system.sessions"));
 
-    // The shardIdentity doc inserted into the admin.system.version collection on the shard.
-    expectShardIdentityUpsertReturnSuccess(shardTarget, expectedShardName);
+    // The shard receives the _addShard command
+    expectAddShardCmdReturnSuccess(shardTarget, expectedShardName);
 
     // The shard receives the setFeatureCompatibilityVersion command.
     expectSetFeatureCompatibilityVersion(
@@ -889,8 +901,8 @@ TEST_F(AddShardTest, SuccessfullyAddReplicaSet) {
 
     expectCollectionDrop(shardTarget, NamespaceString("config", "system.sessions"));
 
-    // The shardIdentity doc inserted into the admin.system.version collection on the shard.
-    expectShardIdentityUpsertReturnSuccess(shardTarget, expectedShardName);
+    // The shard receives the _addShard command
+    expectAddShardCmdReturnSuccess(shardTarget, expectedShardName);
 
     // The shard receives the setFeatureCompatibilityVersion command.
     expectSetFeatureCompatibilityVersion(
@@ -954,8 +966,8 @@ TEST_F(AddShardTest, ReplicaSetExtraHostsDiscovered) {
 
     expectCollectionDrop(shardTarget, NamespaceString("config", "system.sessions"));
 
-    // The shardIdentity doc inserted into the admin.system.version collection on the shard.
-    expectShardIdentityUpsertReturnSuccess(shardTarget, expectedShardName);
+    // The shard receives the _addShard command
+    expectAddShardCmdReturnSuccess(shardTarget, expectedShardName);
 
     // The shard receives the setFeatureCompatibilityVersion command.
     expectSetFeatureCompatibilityVersion(
@@ -1031,8 +1043,8 @@ TEST_F(AddShardTest, AddShardSucceedsEvenIfAddingDBsFromNewShardFails) {
 
     expectCollectionDrop(shardTarget, NamespaceString("config", "system.sessions"));
 
-    // The shardIdentity doc inserted into the admin.system.version collection on the shard.
-    expectShardIdentityUpsertReturnSuccess(shardTarget, expectedShardName);
+    // The shard receives the _addShard command
+    expectAddShardCmdReturnSuccess(shardTarget, expectedShardName);
 
     // The shard receives the setFeatureCompatibilityVersion command.
     expectSetFeatureCompatibilityVersion(
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
index 3bb1bee9a0d..182637837cd 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
@@ -53,6 +53,8 @@
 #include "mongo/db/repl/repl_client_info.h"
 #include "mongo/db/repl/repl_set_config.h"
 #include "mongo/db/repl/replication_coordinator.h"
+#include "mongo/db/s/add_shard_cmd_gen.h"
+#include "mongo/db/s/add_shard_util.h"
 #include "mongo/db/s/type_shard_identity.h"
 #include "mongo/db/wire_version.h"
 #include "mongo/executor/task_executor.h"
@@ -642,21 +644,48 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
         shardType.setMaxSizeMB(maxSize);
     }
 
-    // Insert a shardIdentity document onto the shard. This also triggers sharding initialization on
-    // the shard.
-    LOG(2) << "going to insert shardIdentity document into shard: " << shardType;
-    auto commandRequest = createShardIdentityUpsertForAddShard(opCtx, shardType.getName());
-    auto swCommandResponse =
-        _runCommandForAddShard(opCtx, targeter.get(), NamespaceString::kAdminDb, commandRequest);
-    if (!swCommandResponse.isOK()) {
-        return swCommandResponse.getStatus();
-    }
-    auto commandResponse = std::move(swCommandResponse.getValue());
-    BatchedCommandResponse batchResponse;
-    auto batchResponseStatus =
-        Shard::CommandResponse::processBatchWriteResponse(commandResponse, &batchResponse);
-    if (!batchResponseStatus.isOK()) {
-        return batchResponseStatus;
+    // Helper function that runs a command on the to-be shard and returns the status
+    auto runCmdOnNewShard = [this, &opCtx, &targeter](const BSONObj& cmd) -> Status {
+        auto response =
+            _runCommandForAddShard(opCtx, targeter.get(), NamespaceString::kAdminDb, cmd);
+        // Grabs the underlying status from a StatusWith object by taking the first
+        // non-OK status, if there is one. This is needed due to the semantics of
+        // _runCommandForAddShard.
+        auto commandResponse = std::move(response.getValue());
+        BatchedCommandResponse batchResponse;
+        return Shard::CommandResponse::processBatchWriteResponse(commandResponse, &batchResponse);
+    };
+
+    // Run _addShard command on the shard, which in turn inserts a shardIdentity document onto the
+    // shard and triggers initialization
+    LOG(2) << "going to run _addShard command on shard: " << shardType;
+    AddShard addShardCmd = add_shard_util::createAddShardCmd(opCtx, shardType.getName());
+    BSONObj passthroughFields;  // Needed for IDL toBSON method
+    auto addShardCmdBSON = addShardCmd.toBSON(passthroughFields);
+
+    // Run _addShard command
+    auto addShardStatus = runCmdOnNewShard(addShardCmdBSON);
+
+    if (!addShardStatus.isOK()) {
+        // TODO (SERVER-35552): Fix this to use an FCV check instead
+        // If the _addShard command is not found, that means the mongod for the shard we're adding
+        // is running on an older version, so we retry instead with the old method of inserting a
+        // shard identity document directly.
+        if (addShardStatus == ErrorCodes::CommandNotFound) {
+            // Insert a shardIdentity document onto the shard. This also triggers sharding
+            // initialization on the shard.
+            LOG(2) << AddShard::kCommandName
+                   << " command not found. going to insert shardIdentity document into "
+                      "shard: "
+                   << shardType;
+
+            auto idCommand = add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+            auto shardUpsertCmdStatus = runCmdOnNewShard(idCommand);
+
+            if (!shardUpsertCmdStatus.isOK()) {
+                return shardUpsertCmdStatus;
+            }
+        }
     }
 
     {
@@ -888,33 +917,6 @@ void ShardingCatalogManager::appendConnectionStats(executor::ConnectionPoolStats
     _executorForAddShard->appendConnectionStats(stats);
 }
 
-BSONObj ShardingCatalogManager::createShardIdentityUpsertForAddShard(OperationContext* opCtx,
-                                                                     const std::string& shardName) {
-    BatchedCommandRequest request([&] {
-        write_ops::Update updateOp(NamespaceString::kServerConfigurationNamespace);
-        updateOp.setUpdates(
-            {[&] {
-                write_ops::UpdateOpEntry entry;
-                entry.setQ(BSON("_id"
-                                << "shardIdentity"
-                                << ShardIdentityType::shardName(shardName)
-                                << ShardIdentityType::clusterId(
-                                       ClusterIdentityLoader::get(opCtx)->getClusterId())));
-                entry.setU(BSON("$set" << BSON(ShardIdentityType::configsvrConnString(
-                                    repl::ReplicationCoordinator::get(opCtx)
-                                        ->getConfig()
-                                        .getConnectionString()
-                                        .toString()))));
-                entry.setUpsert(true);
-                return entry;
-            }()});
-        return updateOp;
-    }());
-    request.setWriteConcern(ShardingCatalogClient::kMajorityWriteConcern.toBSON());
-
-    return request.toBSON();
-}
-
 // static
 StatusWith<ShardId> ShardingCatalogManager::_selectShardForNewDatabase(
     OperationContext* opCtx, ShardRegistry* shardRegistry) {
diff --git a/src/mongo/db/s/shard_server_op_observer.cpp b/src/mongo/db/s/shard_server_op_observer.cpp
index 51c9fe954c7..9b8ba53ae89 100644
--- a/src/mongo/db/s/shard_server_op_observer.cpp
+++ b/src/mongo/db/s/shard_server_op_observer.cpp
@@ -211,7 +211,7 @@ void ShardServerOpObserver::onInserts(OperationContext* opCtx,
             if (auto idElem = insertedDoc["_id"]) {
                 if (idElem.str() == ShardIdentityType::IdName) {
                     auto shardIdentityDoc =
-                        uassertStatusOK(ShardIdentityType::fromBSON(insertedDoc));
+                        uassertStatusOK(ShardIdentityType::fromShardIdentityDocument(insertedDoc));
                     uassertStatusOK(shardIdentityDoc.validate());
                     opCtx->recoveryUnit()->registerChange(
                         new ShardIdentityLogOpHandler(opCtx, std::move(shardIdentityDoc)));
diff --git a/src/mongo/db/s/sharding_state.cpp b/src/mongo/db/s/sharding_state.cpp
index 3850454d36f..c45ddb1e71d 100644
--- a/src/mongo/db/s/sharding_state.cpp
+++ b/src/mongo/db/s/sharding_state.cpp
@@ -190,7 +190,7 @@ Status ShardingState::initializeFromShardIdentity(OperationContext* opCtx,
 
     stdx::unique_lock<stdx::mutex> lk(_mutex);
 
-    auto configSvrConnStr = shardIdentity.getConfigsvrConnString();
+    const auto& configSvrConnStr = shardIdentity.getConfigsvrConnectionString();
 
     if (enabled()) {
         invariant(!_shardName.empty());
@@ -241,7 +241,7 @@ Status ShardingState::initializeFromShardIdentity(OperationContext* opCtx,
             _initializationStatus = status;
             _setInitializationState(InitializationState::kError);
         }
-        _shardName = shardIdentity.getShardName();
+        _shardName = shardIdentity.getShardName().toString();
         _clusterId = shardIdentity.getClusterId();
 
         return status;
@@ -275,8 +275,8 @@ StatusWith<bool> ShardingState::initializeShardingAwarenessIfNeeded(OperationCon
                         "If started with --shardsvr in queryableBackupMode, a shardIdentity "
                         "document must be provided through --overrideShardIdentity"};
             }
-            auto swOverrideShardIdentity =
-                ShardIdentityType::fromBSON(serverGlobalParams.overrideShardIdentity);
+            auto swOverrideShardIdentity = ShardIdentityType::fromShardIdentityDocument(
+                serverGlobalParams.overrideShardIdentity);
             if (!swOverrideShardIdentity.isOK()) {
                 return swOverrideShardIdentity.getStatus();
             }
@@ -345,7 +345,7 @@ StatusWith<bool> ShardingState::initializeShardingAwarenessIfNeeded(OperationCon
 
             invariant(!shardIdentityBSON.isEmpty());
 
-            auto swShardIdentity = ShardIdentityType::fromBSON(shardIdentityBSON);
+            auto swShardIdentity = ShardIdentityType::fromShardIdentityDocument(shardIdentityBSON);
             if (!swShardIdentity.isOK()) {
                 return swShardIdentity.getStatus();
             }
diff --git a/src/mongo/db/s/sharding_state_test.cpp b/src/mongo/db/s/sharding_state_test.cpp
index 1b29fe5ceae..94346a3e34d 100644
--- a/src/mongo/db/s/sharding_state_test.cpp
+++ b/src/mongo/db/s/sharding_state_test.cpp
@@ -155,7 +155,7 @@ TEST_F(ShardingStateTest, ValidShardIdentitySucceeds) {
     Lock::GlobalWrite lk(operationContext());
 
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(OID::gen());
@@ -171,7 +171,7 @@ TEST_F(ShardingStateTest, InitWhilePreviouslyInErrorStateWillStayInErrorState) {
     Lock::GlobalWrite lk(operationContext());
 
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(OID::gen());
@@ -209,7 +209,7 @@ TEST_F(ShardingStateTest, InitializeAgainWithMatchingShardIdentitySucceeds) {
 
     auto clusterID = OID::gen();
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(clusterID);
@@ -217,7 +217,7 @@ TEST_F(ShardingStateTest, InitializeAgainWithMatchingShardIdentitySucceeds) {
     ASSERT_OK(shardingState()->initializeFromShardIdentity(operationContext(), shardIdentity));
 
     ShardIdentityType shardIdentity2;
-    shardIdentity2.setConfigsvrConnString(
+    shardIdentity2.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity2.setShardName(kShardName);
     shardIdentity2.setClusterId(clusterID);
@@ -240,7 +240,7 @@ TEST_F(ShardingStateTest, InitializeAgainWithSameReplSetNameSucceeds) {
 
     auto clusterID = OID::gen();
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(clusterID);
@@ -248,7 +248,7 @@ TEST_F(ShardingStateTest, InitializeAgainWithSameReplSetNameSucceeds) {
     ASSERT_OK(shardingState()->initializeFromShardIdentity(operationContext(), shardIdentity));
 
     ShardIdentityType shardIdentity2;
-    shardIdentity2.setConfigsvrConnString(
+    shardIdentity2.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "b:2,c:3", "config"));
     shardIdentity2.setShardName(kShardName);
     shardIdentity2.setClusterId(clusterID);
@@ -281,10 +281,15 @@ TEST_F(ShardingStateTest,
 TEST_F(ShardingStateTest,
        InitializeShardingAwarenessIfNeededReadOnlyAndShardServerAndInvalidOverrideShardIdentity) {
     storageGlobalParams.readOnly = true;
-    serverGlobalParams.overrideShardIdentity = BSON("_id"
-                                                    << "shardIdentity"
-                                                    << "configsvrConnectionString"
-                                                    << "invalid");
+    serverGlobalParams.overrideShardIdentity =
+        BSON("_id"
+             << "shardIdentity"
+             << ShardIdentity::kShardNameFieldName
+             << kShardName
+             << ShardIdentity::kClusterIdFieldName
+             << OID::gen()
+             << ShardIdentity::kConfigsvrConnectionStringFieldName
+             << "invalid");
     auto swShardingInitialized =
         shardingState()->initializeShardingAwarenessIfNeeded(operationContext());
     ASSERT_EQUALS(ErrorCodes::UnsupportedFormat, swShardingInitialized.getStatus().code());
@@ -296,12 +301,12 @@ TEST_F(ShardingStateTest,
     serverGlobalParams.clusterRole = ClusterRole::ShardServer;
 
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(OID::gen());
     ASSERT_OK(shardIdentity.validate());
-    serverGlobalParams.overrideShardIdentity = shardIdentity.toBSON();
+    serverGlobalParams.overrideShardIdentity = shardIdentity.toShardIdentityDocument();
 
     auto swShardingInitialized =
         shardingState()->initializeShardingAwarenessIfNeeded(operationContext());
@@ -343,12 +348,12 @@ TEST_F(ShardingStateTest,
     serverGlobalParams.clusterRole = ClusterRole::None;
 
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(OID::gen());
     ASSERT_OK(shardIdentity.validate());
-    serverGlobalParams.overrideShardIdentity = shardIdentity.toBSON();
+    serverGlobalParams.overrideShardIdentity = shardIdentity.toShardIdentityDocument();
 
     auto swShardingInitialized =
         shardingState()->initializeShardingAwarenessIfNeeded(operationContext());
@@ -380,12 +385,12 @@ TEST_F(ShardingStateTest,
 TEST_F(ShardingStateTest,
        InitializeShardingAwarenessIfNeededNotReadOnlyAndValidOverrideShardIdentity) {
     ShardIdentityType shardIdentity;
-    shardIdentity.setConfigsvrConnString(
+    shardIdentity.setConfigsvrConnectionString(
         ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
     shardIdentity.setShardName(kShardName);
     shardIdentity.setClusterId(OID::gen());
     ASSERT_OK(shardIdentity.validate());
-    serverGlobalParams.overrideShardIdentity = shardIdentity.toBSON();
+    serverGlobalParams.overrideShardIdentity = shardIdentity.toShardIdentityDocument();
 
     // Should error regardless of cluster role.
 
@@ -420,8 +425,13 @@ TEST_F(ShardingStateTest,
 
         BSONObj invalidShardIdentity = BSON("_id"
                                             << "shardIdentity"
-                                            << "configsvrConnectionString"
+                                            << ShardIdentity::kShardNameFieldName
+                                            << kShardName
+                                            << ShardIdentity::kClusterIdFieldName
+                                            << OID::gen()
+                                            << ShardIdentity::kConfigsvrConnectionStringFieldName
                                             << "invalid");
+
         _dbDirectClient->insert(NamespaceString::kServerConfigurationNamespace.toString(),
                                 invalidShardIdentity);
     }
@@ -442,12 +452,12 @@ TEST_F(ShardingStateTest,
 
         BSONObj validShardIdentity = [&] {
             ShardIdentityType shardIdentity;
-            shardIdentity.setConfigsvrConnString(
+            shardIdentity.setConfigsvrConnectionString(
                 ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
             shardIdentity.setShardName(kShardName);
             shardIdentity.setClusterId(OID::gen());
             ASSERT_OK(shardIdentity.validate());
-            return shardIdentity.toBSON();
+            return shardIdentity.toShardIdentityDocument();
         }();
 
         _dbDirectClient->insert(NamespaceString::kServerConfigurationNamespace.toString(),
@@ -496,12 +506,12 @@ TEST_F(ShardingStateTest,
 
     BSONObj validShardIdentity = [&] {
         ShardIdentityType shardIdentity;
-        shardIdentity.setConfigsvrConnString(
+        shardIdentity.setConfigsvrConnectionString(
             ConnectionString(ConnectionString::SET, "a:1,b:2", "config"));
         shardIdentity.setShardName(kShardName);
         shardIdentity.setClusterId(OID::gen());
         ASSERT_OK(shardIdentity.validate());
-        return shardIdentity.toBSON();
+        return shardIdentity.toShardIdentityDocument();
     }();
 
     _dbDirectClient->insert(NamespaceString::kServerConfigurationNamespace.toString(),
diff --git a/src/mongo/db/s/type_shard_identity.cpp b/src/mongo/db/s/type_shard_identity.cpp
index c94fa6e5892..b9e739c3bc9 100644
--- a/src/mongo/db/s/type_shard_identity.cpp
+++ b/src/mongo/db/s/type_shard_identity.cpp
@@ -38,122 +38,46 @@ namespace mongo {
 
 const std::string ShardIdentityType::IdName("shardIdentity");
 
-const BSONField<std::string> ShardIdentityType::configsvrConnString("configsvrConnectionString");
-const BSONField<std::string> ShardIdentityType::shardName("shardName");
-const BSONField<OID> ShardIdentityType::clusterId("clusterId");
-
-StatusWith<ShardIdentityType> ShardIdentityType::fromBSON(const BSONObj& source) {
+StatusWith<ShardIdentityType> ShardIdentityType::fromShardIdentityDocument(const BSONObj& source) {
     if (!source.hasField("_id")) {
         return {ErrorCodes::NoSuchKey,
                 str::stream() << "missing _id field for shardIdentity document"};
     }
-
-    ShardIdentityType shardIdentity;
-
-    {
-        std::string docId;
-        Status status = bsonExtractStringField(source, "_id", &docId);
-        if (!status.isOK()) {
-            return status;
-        }
-
-        if (docId != IdName) {
-            return {ErrorCodes::FailedToParse,
-                    str::stream() << "got _id: " << docId << " instead of " << IdName};
-        }
-    }
-
-    {
-        std::string connString;
-        Status status = bsonExtractStringField(source, configsvrConnString(), &connString);
-        if (!status.isOK()) {
-            return status;
+    // Strip the id field since it's always the same and we don't store it
+    auto shardIdentityBSON = source.removeField("_id");
+
+    try {
+        ShardIdentityType shardIdentity =
+            ShardIdentity::parse(IDLParserErrorContext("ShardIdentity"), shardIdentityBSON);
+
+        const auto& configsvrConnStr = shardIdentity.getConfigsvrConnectionString();
+        if (configsvrConnStr.type() != ConnectionString::SET) {
+            return Status(ErrorCodes::UnsupportedFormat,
+                          str::stream()
+                              << "config server connection string can only be replica sets: "
+                              << configsvrConnStr.toString());
         }
 
-        try {
-            // Note: ConnectionString::parse can uassert from HostAndPort constructor.
-            auto parsedConfigConnStrStatus = ConnectionString::parse(connString);
-            if (!parsedConfigConnStrStatus.isOK()) {
-                return parsedConfigConnStrStatus.getStatus();
-            }
-
-            auto configSvrConnStr = parsedConfigConnStrStatus.getValue();
-            if (configSvrConnStr.type() != ConnectionString::SET) {
-                return Status(ErrorCodes::UnsupportedFormat,
-                              str::stream()
-                                  << "config server connection string can only be replica sets: "
-                                  << configSvrConnStr.toString());
-            }
-
-            shardIdentity.setConfigsvrConnString(std::move(configSvrConnStr));
-        } catch (const AssertionException& parseException) {
-            return parseException.toStatus();
-        }
+        return shardIdentity;
+    } catch (const AssertionException& parseException) {
+        return parseException.toStatus();
     }
-
-    {
-        std::string name;
-        Status status = bsonExtractStringField(source, shardName(), &name);
-        if (!status.isOK()) {
-            return status;
-        }
-
-        shardIdentity.setShardName(name);
-    }
-
-    {
-        OID oid;
-        Status status = bsonExtractOIDField(source, clusterId(), &oid);
-        if (!status.isOK()) {
-            return status;
-        }
-
-        shardIdentity.setClusterId(oid);
-    }
-
-    return shardIdentity;
 }
 
 Status ShardIdentityType::validate() const {
-    if (!_configsvrConnString) {
-        return {ErrorCodes::NoSuchKey,
-                str::stream() << "missing " << configsvrConnString() << " field"};
-    }
-
-    if (_configsvrConnString->type() != ConnectionString::SET) {
+    const auto& configsvrConnStr = getConfigsvrConnectionString();
+    if (configsvrConnStr.type() != ConnectionString::SET) {
         return {ErrorCodes::UnsupportedFormat,
                 str::stream() << "config connection string can only be replica sets, got "
-                              << ConnectionString::typeToString(_configsvrConnString->type())};
-    }
-
-    if (!_shardName || _shardName->empty()) {
-        return {ErrorCodes::NoSuchKey, str::stream() << "missing " << shardName() << " field"};
-    }
-
-    if (!_clusterId || !_clusterId->isSet()) {
-        return {ErrorCodes::NoSuchKey, str::stream() << "missing " << clusterId() << " field"};
+                              << ConnectionString::typeToString(configsvrConnStr.type())};
     }
-
     return Status::OK();
 }
 
-BSONObj ShardIdentityType::toBSON() const {
+BSONObj ShardIdentityType::toShardIdentityDocument() const {
     BSONObjBuilder builder;
-
-    builder.append("_id", IdName);
-
-    if (_configsvrConnString) {
-        builder << configsvrConnString(_configsvrConnString->toString());
-    }
-
-    if (_shardName) {
-        builder << shardName(_shardName.get());
-    }
-
-    if (_clusterId) {
-        builder << clusterId(_clusterId.get());
-    }
-
+    builder.append("_id", ShardIdentityType::IdName);
+    builder.appendElements(ShardIdentity::toBSON());
     return builder.obj();
 }
 
@@ -161,49 +85,10 @@ std::string ShardIdentityType::toString() const {
     return toBSON().toString();
 }
 
-bool ShardIdentityType::isConfigsvrConnStringSet() const {
-    return _configsvrConnString.is_initialized();
-}
-
-const ConnectionString& ShardIdentityType::getConfigsvrConnString() const {
-    invariant(_configsvrConnString);
-    return _configsvrConnString.get();
-}
-
-void ShardIdentityType::setConfigsvrConnString(ConnectionString connString) {
-    _configsvrConnString = std::move(connString);
-}
-
-bool ShardIdentityType::isShardNameSet() const {
-    return _shardName.is_initialized();
-}
-
-const std::string& ShardIdentityType::getShardName() const {
-    invariant(_shardName);
-    return _shardName.get();
-}
-
-void ShardIdentityType::setShardName(std::string shardName) {
-    _shardName = std::move(shardName);
-}
-
-bool ShardIdentityType::isClusterIdSet() const {
-    return _clusterId.is_initialized();
-}
-
-const OID& ShardIdentityType::getClusterId() const {
-    invariant(_clusterId);
-    return _clusterId.get();
-}
-
-void ShardIdentityType::setClusterId(OID clusterId) {
-    _clusterId = std::move(clusterId);
-}
-
 BSONObj ShardIdentityType::createConfigServerUpdateObject(const std::string& newConnString) {
     BSONObjBuilder builder;
     BSONObjBuilder setConfigBuilder(builder.subobjStart("$set"));
-    setConfigBuilder.append(configsvrConnString(), newConnString);
+    setConfigBuilder.append(ShardIdentity::kConfigsvrConnectionStringFieldName, newConnString);
     setConfigBuilder.doneFast();
     return builder.obj();
 }
diff --git a/src/mongo/db/s/type_shard_identity.h b/src/mongo/db/s/type_shard_identity.h
index a46049dd287..b29a8c48a63 100644
--- a/src/mongo/db/s/type_shard_identity.h
+++ b/src/mongo/db/s/type_shard_identity.h
@@ -32,73 +32,48 @@
 
 #include "mongo/client/connection_string.h"
 #include "mongo/db/jsobj.h"
+#include "mongo/db/s/add_shard_cmd_gen.h"
 
 namespace mongo {
 
 /**
  * Contains all the information needed to make a mongod instance shard aware.
  */
-class ShardIdentityType {
+class ShardIdentityType : public ShardIdentity {
 public:
     // The _id value for this document type.
     static const std::string IdName;
 
-    // Field names and types in a shardIdentity document.
-    static const BSONField<std::string> configsvrConnString;
-    static const BSONField<std::string> shardName;
-    static const BSONField<OID> clusterId;
-
     ShardIdentityType() = default;
+    ShardIdentityType(const ShardIdentity& sid) : ShardIdentity(sid) {}
 
     /**
-     * Constructs a new ShardIdentityType object from BSON.
-     * Also does validation of the contents.
-     */
-    static StatusWith<ShardIdentityType> fromBSON(const BSONObj& source);
-
-    /**
-     * Returns OK if all fields have been set. Otherwise, returns NoSuchKey
-     * and information about the first field that is missing.
+     * Constructs a new ShardIdentityType object from a BSON object containing
+     * a shard identity document. Also does validation of the contents.
      */
-    Status validate() const;
+    static StatusWith<ShardIdentityType> fromShardIdentityDocument(const BSONObj& source);
 
     /**
-     * Returns the BSON representation of the entry.
+     * Returns the BSON representation of the entry as a shard identity document.
      */
-    BSONObj toBSON() const;
+    BSONObj toShardIdentityDocument() const;
 
     /**
      * Returns a std::string representation of the current internal state.
      */
     std::string toString() const;
 
-    bool isConfigsvrConnStringSet() const;
-    const ConnectionString& getConfigsvrConnString() const;
-    void setConfigsvrConnString(ConnectionString connString);
-
-    bool isShardNameSet() const;
-    const std::string& getShardName() const;
-    void setShardName(std::string shardName);
-
-    bool isClusterIdSet() const;
-    const OID& getClusterId() const;
-    void setClusterId(OID clusterId);
+    /**
+     * Returns OK if all fields have been set. Otherwise, returns NoSuchKey
+     * and information about the first field that is missing.
+     */
+    Status validate() const;
 
     /**
      * Returns an update object that can be used to update the config server field of the
      * shardIdentity document with the new connection string.
      */
     static BSONObj createConfigServerUpdateObject(const std::string& newConnString);
-
-private:
-    // Convention: (M)andatory, (O)ptional, (S)pecial rule.
-
-    // (M) connection string to the config server.
-    boost::optional<ConnectionString> _configsvrConnString;
-    // (M) contains the name of the shard.
-    boost::optional<std::string> _shardName;
-    // (M) contains the (unique) identifier of the cluster.
-    boost::optional<OID> _clusterId;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/s/type_shard_identity_test.cpp b/src/mongo/db/s/type_shard_identity_test.cpp
index cb9af748106..4fdb1e523de 100644
--- a/src/mongo/db/s/type_shard_identity_test.cpp
+++ b/src/mongo/db/s/type_shard_identity_test.cpp
@@ -43,25 +43,22 @@ TEST(ShardIdentityType, RoundTrip) {
     auto clusterId(OID::gen());
     auto doc = BSON("_id"
                     << "shardIdentity"
-                    << "configsvrConnectionString"
-                    << "test/a:123"
                     << "shardName"
                     << "s1"
                     << "clusterId"
-                    << clusterId);
+                    << clusterId
+                    << "configsvrConnectionString"
+                    << "test/a:123");
 
-    auto result = ShardIdentityType::fromBSON(doc);
+    auto result = ShardIdentityType::fromShardIdentityDocument(doc);
     ASSERT_OK(result.getStatus());
 
     auto shardIdentity = result.getValue();
-    ASSERT_TRUE(shardIdentity.isConfigsvrConnStringSet());
-    ASSERT_EQ("test/a:123", shardIdentity.getConfigsvrConnString().toString());
-    ASSERT_TRUE(shardIdentity.isShardNameSet());
+    ASSERT_EQ("test/a:123", shardIdentity.getConfigsvrConnectionString().toString());
     ASSERT_EQ("s1", shardIdentity.getShardName());
-    ASSERT_TRUE(shardIdentity.isClusterIdSet());
     ASSERT_EQ(clusterId, shardIdentity.getClusterId());
 
-    ASSERT_BSONOBJ_EQ(doc, shardIdentity.toBSON());
+    ASSERT_BSONOBJ_EQ(doc, shardIdentity.toShardIdentityDocument());
 }
 
 TEST(ShardIdentityType, ParseMissingId) {
@@ -72,7 +69,7 @@ TEST(ShardIdentityType, ParseMissingId) {
                     << "clusterId"
                     << OID::gen());
 
-    auto result = ShardIdentityType::fromBSON(doc);
+    auto result = ShardIdentityType::fromShardIdentityDocument(doc);
     ASSERT_NOT_OK(result.getStatus());
 }
 
@@ -84,7 +81,7 @@ TEST(ShardIdentityType, ParseMissingConfigsvrConnString) {
                     << "clusterId"
                     << OID::gen());
 
-    auto result = ShardIdentityType::fromBSON(doc);
+    auto result = ShardIdentityType::fromShardIdentityDocument(doc);
     ASSERT_NOT_OK(result.getStatus());
 }
 
@@ -96,7 +93,7 @@ TEST(ShardIdentityType, ParseMissingShardName) {
                     << "clusterId"
                     << OID::gen());
 
-    auto result = ShardIdentityType::fromBSON(doc);
+    auto result = ShardIdentityType::fromShardIdentityDocument(doc);
     ASSERT_NOT_OK(result.getStatus());
 }
 
@@ -108,7 +105,7 @@ TEST(ShardIdentityType, ParseMissingClusterId) {
                     << "shardName"
                     << "s1");
 
-    auto result = ShardIdentityType::fromBSON(doc);
+    auto result = ShardIdentityType::fromShardIdentityDocument(doc);
     ASSERT_NOT_OK(result.getStatus());
 }
 
@@ -123,7 +120,8 @@ TEST(ShardIdentityType, InvalidConnectionString) {
                     << "clusterId"
                     << clusterId);
 
-    ASSERT_EQ(ErrorCodes::FailedToParse, ShardIdentityType::fromBSON(doc).getStatus());
+    ASSERT_EQ(ErrorCodes::FailedToParse,
+              ShardIdentityType::fromShardIdentityDocument(doc).getStatus());
 }
 
 TEST(ShardIdentityType, NonReplSetConnectionString) {
@@ -137,7 +135,8 @@ TEST(ShardIdentityType, NonReplSetConnectionString) {
                     << "clusterId"
                     << clusterId);
 
-    ASSERT_EQ(ErrorCodes::UnsupportedFormat, ShardIdentityType::fromBSON(doc).getStatus());
+    ASSERT_EQ(ErrorCodes::UnsupportedFormat,
+              ShardIdentityType::fromShardIdentityDocument(doc).getStatus());
 }
 
 TEST(ShardIdentityType, CreateUpdateObject) {