SERVER-72489 Config server always has shardIdentity and uses ShardServerCatalogCacheLoader

18 files changed, 147 insertions, 64 deletions

diff --git a/src/mongo/db/pipeline/sharded_agg_helpers.cpp b/src/mongo/db/pipeline/sharded_agg_helpers.cpp
index dfa0e5452b3..f6c7bb7e6fb 100644
--- a/src/mongo/db/pipeline/sharded_agg_helpers.cpp
+++ b/src/mongo/db/pipeline/sharded_agg_helpers.cpp
@@ -1518,8 +1518,13 @@ StatusWith<CollectionRoutingInfo> getExecutionNsRoutingInfo(OperationContext* op
     // a collection before its enclosing database is created. However, if there are no shards
     // present, then $changeStream should immediately return an empty cursor just as other
     // aggregations do when the database does not exist.
+    //
+    // Note despite config.collections always being unsharded, to support $shardedDataDistribution
+    // we always take the shard targeting path. The collection must only exist on the config server,
+    // so even if there are no shards, the query can still succeed and we shouldn't return
+    // ShardNotFound.
     const auto shardIds = Grid::get(opCtx)->shardRegistry()->getAllShardIds(opCtx);
-    if (shardIds.empty()) {
+    if (shardIds.empty() && execNss != NamespaceString::kConfigsvrCollectionsNamespace) {
         return {ErrorCodes::ShardNotFound, "No shards are present in the cluster"};
     }
 
diff --git a/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp b/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
index e1949b28ac3..3cc920d06cc 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
@@ -43,6 +43,7 @@
 #include "mongo/db/catalog/database_holder.h"
 #include "mongo/db/catalog/drop_collection.h"
 #include "mongo/db/catalog/local_oplog_info.h"
+#include "mongo/db/catalog_shard_feature_flag_gen.h"
 #include "mongo/db/change_stream_change_collection_manager.h"
 #include "mongo/db/change_stream_pre_images_collection_manager.h"
 #include "mongo/db/change_stream_serverless_helpers.h"
@@ -836,11 +837,9 @@ void ReplicationCoordinatorExternalStateImpl::_shardingOnStepDownHook() {
     if (ShardingState::get(_service)->enabled()) {
         ChunkSplitter::get(_service).onStepDown();
         PeriodicBalancerConfigRefresher::get(_service).onStepDown();
+        CatalogCacheLoader::get(_service).onStepDown();
 
         if (serverGlobalParams.clusterRole != ClusterRole::ConfigServer) {
-            // Config shards don't use a loader that requires this.
-            CatalogCacheLoader::get(_service).onStepDown();
-
             // Called earlier for config servers.
             TransactionCoordinatorService::get(_service)->onStepDown();
         }
@@ -945,6 +944,10 @@ void ReplicationCoordinatorExternalStateImpl::_shardingOnTransitionToPrimaryHook
 
         PeriodicShardedIndexConsistencyChecker::get(_service).onStepUp(_service);
         TransactionCoordinatorService::get(_service)->onStepUp(opCtx);
+
+        if (gFeatureFlagCatalogShard.isEnabledAndIgnoreFCV()) {
+            CatalogCacheLoader::get(_service).onStepUp();
+        }
     }
     if (serverGlobalParams.clusterRole == ClusterRole::ShardServer) {
         if (ShardingState::get(opCtx)->enabled()) {
@@ -962,11 +965,9 @@ void ReplicationCoordinatorExternalStateImpl::_shardingOnTransitionToPrimaryHook
 
             ChunkSplitter::get(_service).onStepUp();
             PeriodicBalancerConfigRefresher::get(_service).onStepUp(_service);
+            CatalogCacheLoader::get(_service).onStepUp();
 
             if (serverGlobalParams.clusterRole != ClusterRole::ConfigServer) {
-                // Config shards don't use a loader that requires this.
-                CatalogCacheLoader::get(_service).onStepUp();
-
                 // Called earlier for config servers.
                 TransactionCoordinatorService::get(_service)->onStepUp(opCtx);
             }
@@ -1059,6 +1060,17 @@ void ReplicationCoordinatorExternalStateImpl::_shardingOnTransitionToPrimaryHook
             validator->enableKeyGenerator(opCtx, true);
         }
     }
+
+    if (gFeatureFlagCatalogShard.isEnabled(serverGlobalParams.featureCompatibility) &&
+        serverGlobalParams.clusterRole == ClusterRole::ConfigServer &&
+        !ShardingState::get(opCtx)->enabled()) {
+        // Note this must be called after the config server has created the cluster ID and also
+        // after the onStepUp logic for the shard role because this triggers sharding state
+        // initialization which will transition some components into the "primary" state, like the
+        // TransactionCoordinatorService, and they would fail if the onStepUp logic attempted the
+        // same transition.
+        ShardingCatalogManager::get(opCtx)->installConfigShardIdentityDocument(opCtx);
+    }
 }
 
 void ReplicationCoordinatorExternalStateImpl::signalApplierToChooseNewSyncSource() {
diff --git a/src/mongo/db/s/add_shard_cmd.cpp b/src/mongo/db/s/add_shard_cmd.cpp
index 82b4077f619..d2a48cb784a 100644
--- a/src/mongo/db/s/add_shard_cmd.cpp
+++ b/src/mongo/db/s/add_shard_cmd.cpp
@@ -72,15 +72,15 @@ public:
                          .containsCustomizedGetLastErrorDefaults());
 
             auto addShardCmd = request();
-            auto shardIdUpsertCmd =
-                add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+            auto shardIdUpsertCmd = add_shard_util::createShardIdentityUpsertForAddShard(
+                addShardCmd, ShardingCatalogClient::kMajorityWriteConcern);
             DBDirectClient localClient(opCtx);
             BSONObj res;
 
             localClient.runCommand(
                 DatabaseName(boost::none, NamespaceString::kAdminDb), shardIdUpsertCmd, res);
 
-            uassertStatusOK(getStatusFromCommandResult(res));
+            uassertStatusOK(getStatusFromWriteCommandReply(res));
 
             const auto balancerConfig = Grid::get(opCtx)->getBalancerConfiguration();
             invariant(balancerConfig);
diff --git a/src/mongo/db/s/add_shard_util.cpp b/src/mongo/db/s/add_shard_util.cpp
index 36151320805..a2196828731 100644
--- a/src/mongo/db/s/add_shard_util.cpp
+++ b/src/mongo/db/s/add_shard_util.cpp
@@ -59,7 +59,8 @@ AddShard createAddShardCmd(OperationContext* opCtx, const ShardId& shardName) {
     return addShardCmd;
 }
 
-BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd) {
+BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd,
+                                             const WriteConcernOptions& wc) {
     BatchedCommandRequest request([&] {
         write_ops::UpdateCommandRequest updateOp(NamespaceString::kServerConfigurationNamespace);
         updateOp.setUpdates({[&] {
@@ -73,7 +74,7 @@ BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd) {
 
         return updateOp;
     }());
-    request.setWriteConcern(ShardingCatalogClient::kMajorityWriteConcern.toBSON());
+    request.setWriteConcern(wc.toBSON());
 
     return request.toBSON();
 }
diff --git a/src/mongo/db/s/add_shard_util.h b/src/mongo/db/s/add_shard_util.h
index 020831833ba..7ae28d52dba 100644
--- a/src/mongo/db/s/add_shard_util.h
+++ b/src/mongo/db/s/add_shard_util.h
@@ -32,6 +32,7 @@
 #include <string>
 
 #include "mongo/base/string_data.h"
+#include "mongo/db/write_concern_options.h"
 
 namespace mongo {
 class AddShard;
@@ -58,7 +59,8 @@ AddShard createAddShardCmd(OperationContext* opCtx, const ShardId& shardName);
  * 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);
+BSONObj createShardIdentityUpsertForAddShard(const AddShard& addShardCmd,
+                                             const WriteConcernOptions& wc);
 
 }  // namespace add_shard_util
 }  // namespace mongo
diff --git a/src/mongo/db/s/config/sharding_catalog_manager.h b/src/mongo/db/s/config/sharding_catalog_manager.h
index 3688394efc7..9133b00ed26 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager.h
+++ b/src/mongo/db/s/config/sharding_catalog_manager.h
@@ -483,6 +483,12 @@ public:
                                      const ConnectionString& shardConnectionString);
 
     /**
+     * Inserts the config server shard identity document using a sentinel shard id. Requires the
+     * config server's ShardingState has not already been enabled. Throws on errors.
+     */
+    void installConfigShardIdentityDocument(OperationContext* opCtx);
+
+    /**
      * Tries to remove a shard. To completely remove a shard from a sharded cluster,
      * the data residing in that shard must be moved to the remaining shards in the
      * cluster by "draining" chunks from that shard.
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 bf758421ab9..490a463b29c 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
@@ -50,6 +50,7 @@
 #include "mongo/idl/cluster_server_parameter_common.h"
 #include "mongo/idl/cluster_server_parameter_gen.h"
 #include "mongo/logv2/log.h"
+#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_changelog.h"
 #include "mongo/s/catalog/type_config_version.h"
 #include "mongo/s/catalog/type_database_gen.h"
@@ -370,7 +371,8 @@ protected:
         using namespace add_shard_util;
         // Create the expected upsert shardIdentity command for this shardType.
         auto upsertCmdObj = createShardIdentityUpsertForAddShard(
-            createAddShardCmd(operationContext(), expectedShardName));
+            createAddShardCmd(operationContext(), expectedShardName),
+            ShardingCatalogClient::kMajorityWriteConcern);
 
         const auto opMsgRequest =
             OpMsgRequest::fromDBAndBody(NamespaceString::kAdminDb, upsertCmdObj);
@@ -385,7 +387,8 @@ protected:
         using namespace add_shard_util;
         // Create the expected upsert shardIdentity command for this shardType.
         auto upsertCmdObj = createShardIdentityUpsertForAddShard(
-            createAddShardCmd(operationContext(), expectedShardName));
+            createAddShardCmd(operationContext(), expectedShardName),
+            ShardingCatalogClient::kMajorityWriteConcern);
 
         const auto opMsgRequest =
             OpMsgRequest::fromDBAndBody(NamespaceString::kAdminDb, upsertCmdObj);
@@ -414,8 +417,8 @@ protected:
             auto addShardCmd =
                 AddShard::parse(IDLParserContext(AddShard::kCommandName), addShardOpMsgRequest);
 
-            const auto& updateOpField =
-                add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+            const auto& updateOpField = add_shard_util::createShardIdentityUpsertForAddShard(
+                addShardCmd, ShardingCatalogClient::kMajorityWriteConcern);
 
             const auto updateOpMsgRequest =
                 OpMsgRequest::fromDBAndBody(request.dbname, updateOpField);
@@ -566,7 +569,8 @@ TEST_F(AddShardTest, CreateShardIdentityUpsertForAddShard) {
                      << "majority"
                      << "wtimeout" << 60000));
     auto addShardCmd = add_shard_util::createAddShardCmd(operationContext(), shardName);
-    auto actualBSON = add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
+    auto actualBSON = add_shard_util::createShardIdentityUpsertForAddShard(
+        addShardCmd, ShardingCatalogClient::kMajorityWriteConcern);
     ASSERT_BSONOBJ_EQ(expectedBSON, actualBSON);
 }
 
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 216eab707cd..99cd2dfe0f7 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
@@ -63,6 +63,7 @@
 #include "mongo/db/s/add_shard_cmd_gen.h"
 #include "mongo/db/s/add_shard_util.h"
 #include "mongo/db/s/sharding_logging.h"
+#include "mongo/db/s/sharding_state.h"
 #include "mongo/db/s/type_shard_identity.h"
 #include "mongo/db/s/user_writes_critical_section_document_gen.h"
 #include "mongo/db/s/user_writes_recoverable_critical_section_service.h"
@@ -604,6 +605,26 @@ StatusWith<std::vector<std::string>> ShardingCatalogManager::_getDBNamesListFrom
     return dbNames;
 }
 
+void ShardingCatalogManager::installConfigShardIdentityDocument(OperationContext* opCtx) {
+    invariant(!ShardingState::get(opCtx)->enabled());
+
+    // Insert a shard identity document. Note we insert with local write concern, so the shard
+    // identity may roll back, which will trigger an fassert to clear the in-memory sharding state.
+    {
+        auto addShardCmd = add_shard_util::createAddShardCmd(opCtx, ShardId::kCatalogShardId);
+
+        auto shardIdUpsertCmd = add_shard_util::createShardIdentityUpsertForAddShard(
+            addShardCmd, ShardingCatalogClient::kLocalWriteConcern);
+        DBDirectClient localClient(opCtx);
+        BSONObj res;
+
+        localClient.runCommand(
+            DatabaseName(boost::none, NamespaceString::kAdminDb), shardIdUpsertCmd, res);
+
+        uassertStatusOK(getStatusFromWriteCommandReply(res));
+    }
+}
+
 StatusWith<std::string> ShardingCatalogManager::addShard(
     OperationContext* opCtx,
     const std::string* shardProposedName,
@@ -708,13 +729,18 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
         return Shard::CommandResponse::processBatchWriteResponse(commandResponse, &batchResponse);
     };
 
-    AddShard addShardCmd = add_shard_util::createAddShardCmd(opCtx, shardType.getName());
-
-    // Use the _addShard command to add the shard, which in turn inserts a shardIdentity document
-    // into the shard and triggers sharding state initialization.
-    auto addShardStatus = runCmdOnNewShard(addShardCmd.toBSON({}));
-    if (!addShardStatus.isOK()) {
-        return addShardStatus;
+    // The catalog shard will already have a ShardIdentity document on the config server, so skip
+    // adding it here.
+    if (!gFeatureFlagCatalogShard.isEnabled(serverGlobalParams.featureCompatibility) ||
+        shardType.getName() != ShardId::kCatalogShardId) {
+        AddShard addShardCmd = add_shard_util::createAddShardCmd(opCtx, shardType.getName());
+
+        // Use the _addShard command to add the shard, which in turn inserts a shardIdentity
+        // document into the shard and triggers sharding state initialization.
+        auto addShardStatus = runCmdOnNewShard(addShardCmd.toBSON({}));
+        if (!addShardStatus.isOK()) {
+            return addShardStatus;
+        }
     }
 
     // Set the user-writes blocking state on the new shard.
@@ -974,7 +1000,10 @@ RemoveShardProgress ShardingCatalogManager::removeShard(OperationContext* opCtx,
     // set monitor is removed, otherwise the shard would be referencing a dropped RSM.
     Grid::get(opCtx)->shardRegistry()->reload(opCtx);
 
-    ReplicaSetMonitor::remove(name);
+    if (shardId != ShardId::kCatalogShardId) {
+        // Don't remove the catalog shard's RSM because it is used to target the config server.
+        ReplicaSetMonitor::remove(name);
+    }
 
     // Record finish in changelog
     ShardingLogging::get(opCtx)->logChange(
diff --git a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
index 6264ee66cde..fee6e9cbb46 100644
--- a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
+++ b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
@@ -298,17 +298,24 @@ StatusWith<CollectionAndChangedChunks> getIncompletePersistedMetadataSinceVersio
     }
 }
 
+ShardId getSelfShardId(OperationContext* opCtx) {
+    if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
+        return ShardId::kConfigServerId;
+    }
+
+    auto const shardingState = ShardingState::get(opCtx);
+    invariant(shardingState->enabled());
+    return shardingState->shardId();
+}
+
 /**
  * Sends _flushRoutingTableCacheUpdates to the primary to force it to refresh its routing table for
  * collection 'nss' and then waits for the refresh to replicate to this node.
  */
 void forcePrimaryCollectionRefreshAndWaitForReplication(OperationContext* opCtx,
                                                         const NamespaceString& nss) {
-    auto const shardingState = ShardingState::get(opCtx);
-    invariant(shardingState->enabled());
-
-    auto selfShard = uassertStatusOK(
-        Grid::get(opCtx)->shardRegistry()->getShard(opCtx, shardingState->shardId()));
+    auto selfShard =
+        uassertStatusOK(Grid::get(opCtx)->shardRegistry()->getShard(opCtx, getSelfShardId(opCtx)));
 
     auto cmdResponse = uassertStatusOK(selfShard->runCommandWithFixedRetryAttempts(
         opCtx,
@@ -329,11 +336,8 @@ void forcePrimaryCollectionRefreshAndWaitForReplication(OperationContext* opCtx,
  * database 'dbName' and then waits for the refresh to replicate to this node.
  */
 void forcePrimaryDatabaseRefreshAndWaitForReplication(OperationContext* opCtx, StringData dbName) {
-    auto const shardingState = ShardingState::get(opCtx);
-    invariant(shardingState->enabled());
-
-    auto selfShard = uassertStatusOK(
-        Grid::get(opCtx)->shardRegistry()->getShard(opCtx, shardingState->shardId()));
+    auto selfShard =
+        uassertStatusOK(Grid::get(opCtx)->shardRegistry()->getShard(opCtx, getSelfShardId(opCtx)));
 
     auto cmdResponse = uassertStatusOK(selfShard->runCommandWithFixedRetryAttempts(
         opCtx,
@@ -424,6 +428,14 @@ void ShardServerCatalogCacheLoader::shutDown() {
 
 SemiFuture<CollectionAndChangedChunks> ShardServerCatalogCacheLoader::getChunksSince(
     const NamespaceString& nss, ChunkVersion version) {
+    // There's no need to refresh if a collection is always unsharded. Further, attempting to refesh
+    // config.collections or config.chunks would trigger recursive refreshes, and, if this is
+    // running on a config server secondary, the refresh would not succeed if the primary is
+    // unavailable, unnecessarily reducing availability.
+    if (nss.isNamespaceAlwaysUnsharded()) {
+        return Status(ErrorCodes::NamespaceNotFound,
+                      str::stream() << "Collection " << nss.ns() << " not found");
+    }
 
     bool isPrimary;
     long long term;
diff --git a/src/mongo/db/s/sharding_ddl_coordinator.cpp b/src/mongo/db/s/sharding_ddl_coordinator.cpp
index 4d53f6e7984..62b1e4eef44 100644
--- a/src/mongo/db/s/sharding_ddl_coordinator.cpp
+++ b/src/mongo/db/s/sharding_ddl_coordinator.cpp
@@ -266,7 +266,7 @@ SemiFuture<void> ShardingDDLCoordinator::run(std::shared_ptr<executor::ScopedTas
             return _acquireLockAsync(executor, token, originalNss().db());
         })
         .then([this, executor, token, anchor = shared_from_this()] {
-            if (!originalNss().isConfigDB() && !_recoveredFromDisk) {
+            if (!originalNss().isConfigDB() && !originalNss().isAdminDB() && !_recoveredFromDisk) {
                 auto opCtxHolder = cc().makeOperationContext();
                 auto* opCtx = opCtxHolder.get();
                 invariant(metadata().getDatabaseVersion());
diff --git a/src/mongo/db/s/sharding_ddl_coordinator_service.cpp b/src/mongo/db/s/sharding_ddl_coordinator_service.cpp
index fa8c1b8e66e..77799dbd322 100644
--- a/src/mongo/db/s/sharding_ddl_coordinator_service.cpp
+++ b/src/mongo/db/s/sharding_ddl_coordinator_service.cpp
@@ -263,7 +263,7 @@ ShardingDDLCoordinatorService::getOrCreateInstance(OperationContext* opCtx, BSON
     auto coorMetadata = extractShardingDDLCoordinatorMetadata(coorDoc);
     const auto& nss = coorMetadata.getId().getNss();
 
-    if (!nss.isConfigDB()) {
+    if (!nss.isConfigDB() && !nss.isAdminDB()) {
         // Check that the operation context has a database version for this namespace
         const auto clientDbVersion = OperationShardingState::get(opCtx).getDbVersion(nss.db());
         uassert(ErrorCodes::IllegalOperation,
diff --git a/src/mongo/db/s/sharding_initialization_mongod.cpp b/src/mongo/db/s/sharding_initialization_mongod.cpp
index 2e7f0dac299..2c2121bb0db 100644
--- a/src/mongo/db/s/sharding_initialization_mongod.cpp
+++ b/src/mongo/db/s/sharding_initialization_mongod.cpp
@@ -41,6 +41,7 @@
 #include "mongo/db/catalog_shard_feature_flag_gen.h"
 #include "mongo/db/client_metadata_propagation_egress_hook.h"
 #include "mongo/db/concurrency/d_concurrency.h"
+#include "mongo/db/concurrency/replication_state_transition_lock_guard.h"
 #include "mongo/db/dbhelpers.h"
 #include "mongo/db/keys_collection_client_direct.h"
 #include "mongo/db/keys_collection_client_sharded.h"
@@ -557,7 +558,23 @@ void initializeGlobalShardingStateForConfigServerIfNeeded(OperationContext* opCt
         return {ConnectionString::forLocal()};
     }();
 
-    CatalogCacheLoader::set(service, std::make_unique<ConfigServerCatalogCacheLoader>());
+    if (gFeatureFlagCatalogShard.isEnabledAndIgnoreFCV()) {
+        CatalogCacheLoader::set(service,
+                                std::make_unique<ShardServerCatalogCacheLoader>(
+                                    std::make_unique<ConfigServerCatalogCacheLoader>()));
+
+        // This is only called in startup when there shouldn't be replication state changes, but to
+        // be safe we take the RSTL anyway.
+        repl::ReplicationStateTransitionLockGuard rstl(opCtx, MODE_IX);
+        const auto replCoord = repl::ReplicationCoordinator::get(opCtx);
+        bool isReplSet =
+            replCoord->getReplicationMode() == repl::ReplicationCoordinator::modeReplSet;
+        bool isStandaloneOrPrimary =
+            !isReplSet || (replCoord->getMemberState() == repl::MemberState::RS_PRIMARY);
+        CatalogCacheLoader::get(opCtx).initializeReplicaSetRole(isStandaloneOrPrimary);
+    } else {
+        CatalogCacheLoader::set(service, std::make_unique<ConfigServerCatalogCacheLoader>());
+    }
 
     initializeGlobalShardingStateForMongoD(opCtx, configCS);
 
diff --git a/src/mongo/db/shard_id.cpp b/src/mongo/db/shard_id.cpp
index 39d66aa56a7..445abe37baa 100644
--- a/src/mongo/db/shard_id.cpp
+++ b/src/mongo/db/shard_id.cpp
@@ -35,6 +35,9 @@ namespace mongo {
 
 const ShardId ShardId::kConfigServerId("config");
 
+// TODO SERVER-XXXXX: Use "config" shard id instead.
+const ShardId ShardId::kCatalogShardId("catalogShard");
+
 bool ShardId::isValid() const {
     return !_shardId.empty();
 }
diff --git a/src/mongo/db/shard_id.h b/src/mongo/db/shard_id.h
index 798f8e427a1..b99469d1459 100644
--- a/src/mongo/db/shard_id.h
+++ b/src/mongo/db/shard_id.h
@@ -43,6 +43,7 @@ namespace mongo {
 class ShardId {
 public:
     static const ShardId kConfigServerId;
+    static const ShardId kCatalogShardId;
 
     ShardId(std::string shardId) : _shardId(std::move(shardId)) {}
 
diff --git a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
index b2a052fee22..c2c1a0c6817 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
@@ -732,12 +732,6 @@ std::pair<CollectionType, std::vector<ChunkType>> ShardingCatalogClientImpl::get
     const NamespaceString& nss,
     const ChunkVersion& sinceVersion,
     const repl::ReadConcernArgs& readConcern) {
-    // The config.collections collection is always unsharded. Attempting to run the aggregation
-    // pipeline on it will trigger recursive refreshes, so return NamespaceNotFound right away.
-    uassert(ErrorCodes::NamespaceNotFound,
-            str::stream() << "Collection " << nss.ns() << " not found",
-            nss != NamespaceString::kConfigsvrCollectionsNamespace);
-
     auto aggRequest = makeCollectionAndChunksAggregation(opCtx, nss, sinceVersion);
 
     std::vector<BSONObj> aggResult =
diff --git a/src/mongo/s/client/shard_registry.cpp b/src/mongo/s/client/shard_registry.cpp
index c9b58cf8997..77e02f641c6 100644
--- a/src/mongo/s/client/shard_registry.cpp
+++ b/src/mongo/s/client/shard_registry.cpp
@@ -188,7 +188,10 @@ ShardRegistry::Cache::LookupResult ShardRegistry::_lookup(OperationContext* opCt
         invariant(shard);
 
         auto name = shard->getConnString().getSetName();
-        ReplicaSetMonitor::remove(name);
+        if (shardId != ShardId::kCatalogShardId) {
+            // Don't remove the catalog shard's RSM because it is used to target the config server.
+            ReplicaSetMonitor::remove(name);
+        }
         _removeReplicaSet(name);
         for (auto& callback : _shardRemovalHooks) {
             // Run callbacks asynchronously.
diff --git a/src/mongo/s/config_server_catalog_cache_loader.cpp b/src/mongo/s/config_server_catalog_cache_loader.cpp
index 8b3736e79c5..899b7299132 100644
--- a/src/mongo/s/config_server_catalog_cache_loader.cpp
+++ b/src/mongo/s/config_server_catalog_cache_loader.cpp
@@ -111,29 +111,17 @@ void ConfigServerCatalogCacheLoader::shutDown() {
 }
 
 void ConfigServerCatalogCacheLoader::notifyOfCollectionVersionUpdate(const NamespaceString& nss) {
-    // TODO SERVER-72489: Restore MONGO_UNREACHABLE if we decide to use a
-    // ShardServerCatalogCacheLoader on the catalog shard.
-    if (!gFeatureFlagCatalogShard.isEnabledAndIgnoreFCV()) {
-        MONGO_UNREACHABLE;
-    }
+    MONGO_UNREACHABLE;
 }
 
 void ConfigServerCatalogCacheLoader::waitForCollectionFlush(OperationContext* opCtx,
                                                             const NamespaceString& nss) {
-    // TODO SERVER-72489: Restore MONGO_UNREACHABLE if we decide to use a
-    // ShardServerCatalogCacheLoader on the catalog shard.
-    if (!gFeatureFlagCatalogShard.isEnabledAndIgnoreFCV()) {
-        MONGO_UNREACHABLE;
-    }
+    MONGO_UNREACHABLE;
 }
 
 void ConfigServerCatalogCacheLoader::waitForDatabaseFlush(OperationContext* opCtx,
                                                           StringData dbName) {
-    // TODO SERVER-72489: Restore MONGO_UNREACHABLE if we decide to use a
-    // ShardServerCatalogCacheLoader on the catalog shard.
-    if (!gFeatureFlagCatalogShard.isEnabledAndIgnoreFCV()) {
-        MONGO_UNREACHABLE;
-    }
+    MONGO_UNREACHABLE;
 }
 
 SemiFuture<CollectionAndChangedChunks> ConfigServerCatalogCacheLoader::getChunksSince(
diff --git a/src/mongo/shell/shardingtest.js b/src/mongo/shell/shardingtest.js
index 19547df7589..de6dcf93c3a 100644
--- a/src/mongo/shell/shardingtest.js
+++ b/src/mongo/shell/shardingtest.js
@@ -1811,13 +1811,19 @@ var ShardingTest = function(params) {
             var testName = this._testName;
             var admin = this.admin;
 
-            this._connections.forEach(function(z) {
+            this._connections.forEach(function(z, idx) {
                 var n = z.name || z.host || z;
 
+                var name;
+                if (isCatalogShardMode && idx == 0) {
+                    name = "catalogShard";
+                }
+
                 print("ShardingTest " + testName + " going to add shard : " + n);
 
-                var result = assert.commandWorked(admin.runCommand({addshard: n}),
-                                                  "Failed to add shard " + n);
+                var result = assert.commandWorked(
+                    admin.runCommand(name ? {addshard: n, name: name} : {addshard: n}),
+                    "Failed to add shard " + n);
                 z.shardName = result.shardAdded;
             });
         }