SERVER-49242 Add serverStatus counters for number of running PrimaryOnlyService instances

5 files changed, 74 insertions, 8 deletions

diff --git a/src/mongo/db/repl/SConscript b/src/mongo/db/repl/SConscript
index eeddbed7948..0ef88b0a410 100644
--- a/src/mongo/db/repl/SConscript
+++ b/src/mongo/db/repl/SConscript
@@ -1232,6 +1232,7 @@ env.Library(
         '$BUILD_DIR/mongo/db/repl/speculative_authenticate',
         '$BUILD_DIR/mongo/db/stats/counters',
         '$BUILD_DIR/mongo/transport/message_compressor',
+        'primary_only_service',
         'replication_auth',
         'split_horizon',
     ],
diff --git a/src/mongo/db/repl/primary_only_service.cpp b/src/mongo/db/repl/primary_only_service.cpp
index acf79190d1b..ab7f25ec861 100644
--- a/src/mongo/db/repl/primary_only_service.cpp
+++ b/src/mongo/db/repl/primary_only_service.cpp
@@ -227,9 +227,21 @@ void PrimaryOnlyServiceRegistry::onStepDown() {
     }
 }
 
+void PrimaryOnlyServiceRegistry::reportServiceInfo(BSONObjBuilder* result) {
+    BSONObjBuilder subBuilder(result->subobjStart("primaryOnlyServices"));
+    for (auto& service : _servicesByName) {
+        subBuilder.appendNumber(service.first, service.second->getNumberOfInstances());
+    }
+}
+
 PrimaryOnlyService::PrimaryOnlyService(ServiceContext* serviceContext)
     : _serviceContext(serviceContext) {}
 
+size_t PrimaryOnlyService::getNumberOfInstances() {
+    stdx::lock_guard lk(_mutex);
+    return _instances.size();
+}
+
 bool PrimaryOnlyService::isRunning() const {
     stdx::lock_guard lk(_mutex);
     return _state == State::kRunning;
diff --git a/src/mongo/db/repl/primary_only_service.h b/src/mongo/db/repl/primary_only_service.h
index 0d57cf96d9b..664ecd9fa11 100644
--- a/src/mongo/db/repl/primary_only_service.h
+++ b/src/mongo/db/repl/primary_only_service.h
@@ -217,6 +217,11 @@ public:
      */
     bool isRunning() const;
 
+    /**
+     * Returns the number of currently running Instances of this service.
+     */
+    size_t getNumberOfInstances();
+
 protected:
     /**
      * Constructs a new Instance object with the given initial state.
@@ -328,6 +333,12 @@ public:
      */
     PrimaryOnlyService* lookupServiceByNamespace(const NamespaceString& ns);
 
+    /**
+     * Adds a 'primaryOnlyServices' sub-obj to the 'result' BSONObjBuilder containing a count of the
+     * number of active instances for each registered service.
+     */
+    void reportServiceInfo(BSONObjBuilder* result);
+
     void onStartup(OperationContext*) final;
     void onShutdown() final;
     void onStepUpBegin(OperationContext*, long long term) final {}
diff --git a/src/mongo/db/repl/primary_only_service_test.cpp b/src/mongo/db/repl/primary_only_service_test.cpp
index d89005e8b1d..d7c76b6b7cb 100644
--- a/src/mongo/db/repl/primary_only_service_test.cpp
+++ b/src/mongo/db/repl/primary_only_service_test.cpp
@@ -367,6 +367,40 @@ TEST_F(PrimaryOnlyServiceTest, DoubleCreateInstance) {
     TestServiceHangDuringInitialization.setMode(FailPoint::off);
 }
 
+TEST_F(PrimaryOnlyServiceTest, ReportServiceInfo) {
+    {
+        BSONObjBuilder resultBuilder;
+        _registry->reportServiceInfo(&resultBuilder);
+
+        ASSERT_BSONOBJ_EQ(BSON("primaryOnlyServices" << BSON("TestService" << 0)),
+                          resultBuilder.obj());
+    }
+
+    // Make sure the instance doesn't complete.
+    TestServiceHangDuringInitialization.setMode(FailPoint::alwaysOn);
+    auto instance = TestService::Instance::getOrCreate(_service, BSON("_id" << 0 << "state" << 0));
+
+    {
+        BSONObjBuilder resultBuilder;
+        _registry->reportServiceInfo(&resultBuilder);
+
+        ASSERT_BSONOBJ_EQ(BSON("primaryOnlyServices" << BSON("TestService" << 1)),
+                          resultBuilder.obj());
+    }
+
+    auto instance2 = TestService::Instance::getOrCreate(_service, BSON("_id" << 1 << "state" << 0));
+
+    {
+        BSONObjBuilder resultBuilder;
+        _registry->reportServiceInfo(&resultBuilder);
+
+        ASSERT_BSONOBJ_EQ(BSON("primaryOnlyServices" << BSON("TestService" << 2)),
+                          resultBuilder.obj());
+    }
+
+    TestServiceHangDuringInitialization.setMode(FailPoint::off);
+}
+
 TEST_F(PrimaryOnlyServiceTest, CreateWhenNotPrimary) {
     _registry->onStepDown();
 
diff --git a/src/mongo/db/repl/replication_info.cpp b/src/mongo/db/repl/replication_info.cpp
index ec551d390ea..188de5e8d16 100644
--- a/src/mongo/db/repl/replication_info.cpp
+++ b/src/mongo/db/repl/replication_info.cpp
@@ -50,6 +50,7 @@
 #include "mongo/db/ops/write_ops.h"
 #include "mongo/db/query/internal_plans.h"
 #include "mongo/db/repl/is_master_response.h"
+#include "mongo/db/repl/primary_only_service.h"
 #include "mongo/db/repl/replication_auth.h"
 #include "mongo/db/repl/replication_coordinator.h"
 #include "mongo/db/repl/replication_process.h"
@@ -86,12 +87,17 @@ constexpr auto kHelloString = "hello"_sd;
 constexpr auto kCamelCaseIsMasterString = "isMaster"_sd;
 constexpr auto kLowerCaseIsMasterString = "ismaster"_sd;
 
+void appendPrimaryOnlyServiceInfo(ServiceContext* serviceContext, BSONObjBuilder* result) {
+    auto registry = PrimaryOnlyServiceRegistry::get(serviceContext);
+    registry->reportServiceInfo(result);
+}
+
 /**
  * Appends replication-related fields to the isMaster response. Returns the topology version that
  * was included in the response.
  */
 TopologyVersion appendReplicationInfo(OperationContext* opCtx,
-                                      BSONObjBuilder& result,
+                                      BSONObjBuilder* result,
                                       bool appendReplicationProcess,
                                       bool useLegacyResponseFields,
                                       boost::optional<TopologyVersion> clientTopologyVersion,
@@ -108,9 +114,9 @@ TopologyVersion appendReplicationInfo(OperationContext* opCtx,
         }
         auto isMasterResponse =
             replCoord->awaitIsMasterResponse(opCtx, horizonParams, clientTopologyVersion, deadline);
-        result.appendElements(isMasterResponse->toBSON(useLegacyResponseFields));
+        result->appendElements(isMasterResponse->toBSON(useLegacyResponseFields));
         if (appendReplicationProcess) {
-            replCoord->appendSlaveInfoData(&result);
+            replCoord->appendSlaveInfoData(result);
         }
         invariant(isMasterResponse->getTopologyVersion());
         return isMasterResponse->getTopologyVersion().get();
@@ -142,10 +148,10 @@ TopologyVersion appendReplicationInfo(OperationContext* opCtx,
         opCtx->sleepFor(Milliseconds(*maxAwaitTimeMS));
     }
 
-    result.appendBool((useLegacyResponseFields ? "ismaster" : "isWritablePrimary"),
-                      ReplicationCoordinator::get(opCtx)->isMasterForReportingPurposes());
+    result->appendBool((useLegacyResponseFields ? "ismaster" : "isWritablePrimary"),
+                       ReplicationCoordinator::get(opCtx)->isMasterForReportingPurposes());
 
-    BSONObjBuilder topologyVersionBuilder(result.subobjStart("topologyVersion"));
+    BSONObjBuilder topologyVersionBuilder(result->subobjStart("topologyVersion"));
     currentTopologyVersion.serialize(&topologyVersionBuilder);
 
     return currentTopologyVersion;
@@ -171,12 +177,14 @@ public:
         // TODO SERVER-50219: Change useLegacyResponseFields to false once the serverStatus changes
         // to remove master-slave terminology are merged.
         appendReplicationInfo(opCtx,
-                              result,
+                              &result,
                               appendReplicationProcess,
                               true /* useLegacyResponseFields */,
                               boost::none /* clientTopologyVersion */,
                               boost::none /* maxAwaitTimeMS */);
 
+        appendPrimaryOnlyServiceInfo(opCtx->getServiceContext(), &result);
+
         auto rbid = ReplicationProcess::get(opCtx)->getRollbackID();
         if (ReplicationProcess::kUninitializedRollbackId != rbid) {
             result.append("rbid", rbid);
@@ -426,7 +434,7 @@ public:
 
         auto result = replyBuilder->getBodyBuilder();
         auto currentTopologyVersion = appendReplicationInfo(
-            opCtx, result, 0, useLegacyResponseFields, clientTopologyVersion, maxAwaitTimeMS);
+            opCtx, &result, 0, useLegacyResponseFields, clientTopologyVersion, maxAwaitTimeMS);
 
         if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
             const int configServerModeNumber = 2;