SERVER-56846 Fail reconfig for shard server if it would change DWCF and CWWC is not set

6 files changed, 70 insertions, 18 deletions

diff --git a/src/mongo/db/repl/replication_coordinator_external_state.h b/src/mongo/db/repl/replication_coordinator_external_state.h
index 02b8e71ef20..3fb2ecfc61a 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state.h
+++ b/src/mongo/db/repl/replication_coordinator_external_state.h
@@ -328,6 +328,12 @@ public:
      * Assert will be raised if running a command on the config server failed.
      */
     virtual bool isCWWCSetOnConfigShard(OperationContext* opCtx) const = 0;
+
+    /**
+     * Used to check if the server is a shardServer and has been added to a sharded cluster via
+     * addShard.
+     */
+    virtual bool isShardPartOfShardedCluster(OperationContext* opCtx) const = 0;
 };
 
 }  // namespace repl
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 23606fedb07..36c740ffa57 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
@@ -1132,6 +1132,12 @@ void ReplicationCoordinatorExternalStateImpl::setupNoopWriter(Seconds waitTime)
     _noopWriter = std::make_unique<NoopWriter>(waitTime);
 }
 
+bool ReplicationCoordinatorExternalStateImpl::isShardPartOfShardedCluster(
+    OperationContext* opCtx) const {
+    return serverGlobalParams.clusterRole == ClusterRole::ShardServer &&
+        ShardingState::get(opCtx)->enabled();
+}
+
 bool ReplicationCoordinatorExternalStateImpl::isCWWCSetOnConfigShard(
     OperationContext* opCtx) const {
     GetDefaultRWConcern configsvrRequest;
diff --git a/src/mongo/db/repl/replication_coordinator_external_state_impl.h b/src/mongo/db/repl/replication_coordinator_external_state_impl.h
index 62fa04c7caf..39d684a55e3 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_impl.h
+++ b/src/mongo/db/repl/replication_coordinator_external_state_impl.h
@@ -123,6 +123,8 @@ public:
 
     virtual bool isCWWCSetOnConfigShard(OperationContext* opCtx) const final;
 
+    virtual bool isShardPartOfShardedCluster(OperationContext* opCtx) const final;
+
 private:
     /**
      * Stops data replication and returns with 'lock' locked.
diff --git a/src/mongo/db/repl/replication_coordinator_external_state_mock.cpp b/src/mongo/db/repl/replication_coordinator_external_state_mock.cpp
index dc25c08fb9c..d2607393528 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_mock.cpp
+++ b/src/mongo/db/repl/replication_coordinator_external_state_mock.cpp
@@ -322,5 +322,10 @@ bool ReplicationCoordinatorExternalStateMock::isCWWCSetOnConfigShard(
     return true;
 }
 
+bool ReplicationCoordinatorExternalStateMock::isShardPartOfShardedCluster(
+    OperationContext* opCtx) const {
+    return true;
+}
+
 }  // namespace repl
 }  // namespace mongo
diff --git a/src/mongo/db/repl/replication_coordinator_external_state_mock.h b/src/mongo/db/repl/replication_coordinator_external_state_mock.h
index fb74a55e2e3..22b2a7444b7 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_mock.h
+++ b/src/mongo/db/repl/replication_coordinator_external_state_mock.h
@@ -198,6 +198,8 @@ public:
 
     virtual bool isCWWCSetOnConfigShard(OperationContext* opCtx) const final;
 
+    virtual bool isShardPartOfShardedCluster(OperationContext* opCtx) const final;
+
 private:
     StatusWith<BSONObj> _localRsConfigDocument;
     StatusWith<LastVote> _localRsLastVoteDocument;
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 15c39da1255..32c95fdaf50 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -3502,26 +3502,57 @@ Status ReplicationCoordinatorImpl::_doReplSetReconfig(OperationContext* opCtx,
         return status;
     ReplSetConfig newConfig = newConfigStatus.getValue();
 
-    // If the new config changes the replica set's implicit default write concern, we fail the
-    // reconfig command. This includes force reconfigs, but excludes reconfigs that bump the config
-    // term during step-up. The user should set a cluster-wide write concern and attempt the
-    // reconfig command again. We also need to exclude shard servers from this validation, as shard
-    // servers don't store the cluster-wide write concern.
-    if (!skipSafetyChecks /* skipping step-up reconfig */ &&
-        repl::feature_flags::gDefaultWCMajority.isEnabled(
-            serverGlobalParams.featureCompatibility) &&
-        serverGlobalParams.clusterRole != ClusterRole::ShardServer &&
-        !repl::enableDefaultWriteConcernUpdatesForInitiate.load()) {
+    // Excluding reconfigs that bump the config term during step-up from checking against changing
+    // the implicit default write concern, as it is not needed.
+    if (!skipSafetyChecks /* skipping step-up reconfig */) {
         bool currIDWC = oldConfig.isImplicitDefaultWriteConcernMajority();
         bool newIDWC = newConfig.isImplicitDefaultWriteConcernMajority();
-        bool isCWWCSet = ReadWriteConcernDefaults::get(opCtx).isCWWCSet(opCtx);
-        if (!isCWWCSet && currIDWC != newIDWC) {
-            return Status(
-                ErrorCodes::NewReplicaSetConfigurationIncompatible,
-                str::stream()
-                    << "Reconfig attempted to install a config that would change the "
-                       "implicit default write concern. Use the setDefaultRWConcern command to "
-                       "set a cluster-wide write concern and try the reconfig again.");
+
+        // If the new config changes the replica set's implicit default write concern, we fail the
+        // reconfig command. This includes force reconfigs.
+        // The user should set a cluster-wide write concern and attempt the reconfig command again.
+        if (serverGlobalParams.clusterRole != ClusterRole::ShardServer) {
+            if (repl::feature_flags::gDefaultWCMajority.isEnabled(
+                    serverGlobalParams.featureCompatibility) &&
+                !repl::enableDefaultWriteConcernUpdatesForInitiate.load() && currIDWC != newIDWC &&
+                !ReadWriteConcernDefaults::get(opCtx).isCWWCSet(opCtx)) {
+                return Status(
+                    ErrorCodes::NewReplicaSetConfigurationIncompatible,
+                    str::stream()
+                        << "Reconfig attempted to install a config that would change the implicit "
+                           "default write concern. Use the setDefaultRWConcern command to set a "
+                           "cluster-wide write concern and try the reconfig again.");
+            }
+        } else {
+            // Allow all reconfigs if the shard is not part of a sharded cluster yet, however
+            // prevent changing the implicit default write concern to (w: 1) after it becomes part
+            // of a sharded cluster and CWWC is not set on the cluster.
+            // Remote call to the configServer should be done to check if CWWC is set on the
+            // cluster.
+            if (_externalState->isShardPartOfShardedCluster(opCtx) && currIDWC != newIDWC &&
+                !newIDWC) {
+                try {
+                    // Initiates a remote call to the config server.
+                    if (!_externalState->isCWWCSetOnConfigShard(opCtx)) {
+                        return Status(
+                            ErrorCodes::NewReplicaSetConfigurationIncompatible,
+                            str::stream()
+                                << "Reconfig attempted to install a config that would change the "
+                                   "implicit default write concern on the shard to {w: 1}. Use the "
+                                   "setDefaultRWConcern command to set a cluster-wide write "
+                                   "concern on the cluster and try the reconfig again.");
+                    }
+                } catch (const DBException& ex) {
+                    return Status(
+                        ErrorCodes::ConfigServerUnreachable,
+                        str::stream()
+                            << "Reconfig attempted to install a config that would change the "
+                               "implicit default write concern on the shard to {w: 1}, but the "
+                               "shard can not check if CWWC is set on the cluster, as the request "
+                               "to the config server is failing with error: " +
+                                ex.toString());
+                }
+            }
         }
     }