fix: add a metric to track client registrations (#9314)

Adding a counter to track every time a client registers with Unleash.

src/lib/features/metrics/instance/instance-service.ts

@@ -1,3 +1,4 @@
+import type EventEmitter from 'events';
 import { APPLICATION_CREATED, CLIENT_REGISTER } from '../../../types/events';
 import type { IApplication, IApplicationOverview } from './models';
 import type { IUnleashStores } from '../../../types/stores';
@@ -24,6 +25,7 @@ import { ALL_PROJECTS, parseStrictSemVer } from '../../../util';
 import type { Logger } from '../../../logger';
 import { findOutdatedSDKs, isOutdatedSdk } from './findOutdatedSdks';
 import type { OutdatedSdksSchema } from '../../../openapi/spec/outdated-sdks-schema';
+import { CLIENT_REGISTERED } from '../../../metric-events';
 
 export default class ClientInstanceService {
     apps = {};
@@ -48,6 +50,8 @@ export default class ClientInstanceService {
 
     private flagResolver: IFlagResolver;
 
+    private eventBus: EventEmitter;
+
     constructor(
         {
             clientMetricsStoreV2,
@@ -68,7 +72,8 @@ export default class ClientInstanceService {
         {
             getLogger,
             flagResolver,
-        }: Pick<IUnleashConfig, 'getLogger' | 'flagResolver'>,
+            eventBus,
+        }: Pick<IUnleashConfig, 'getLogger' | 'flagResolver' | 'eventBus'>,
         privateProjectChecker: IPrivateProjectChecker,
     ) {
         this.clientMetricsStoreV2 = clientMetricsStoreV2;
@@ -77,6 +82,7 @@ export default class ClientInstanceService {
         this.clientApplicationsStore = clientApplicationsStore;
         this.clientInstanceStore = clientInstanceStore;
         this.eventStore = eventStore;
+        this.eventBus = eventBus;
         this.privateProjectChecker = privateProjectChecker;
         this.flagResolver = flagResolver;
         this.logger = getLogger(
@@ -105,6 +111,7 @@ export default class ClientInstanceService {
         value.clientIp = clientIp;
         value.createdBy = SYSTEM_USER.username!;
         this.seenClients[this.clientKey(value)] = value;
+        this.eventBus.emit(CLIENT_REGISTERED, value);
 
         if (value.sdkVersion && value.sdkVersion.indexOf(':') > -1) {
             const [sdkName, sdkVersion] = value.sdkVersion.split(':');

src/lib/metric-events.ts

@@ -19,6 +19,7 @@ const CLIENT_METRICS_NAMEPREFIX = 'client-api-nameprefix';
 const CLIENT_METRICS_TAGS = 'client-api-tags';
 const CLIENT_FEATURES_MEMORY = 'client_features_memory';
 const CLIENT_DELTA_MEMORY = 'client_delta_memory';
+const CLIENT_REGISTERED = 'client_registered';
 
 type MetricEvent =
     | typeof REQUEST_TIME
@@ -91,6 +92,7 @@ export {
     CLIENT_METRICS_TAGS,
     CLIENT_FEATURES_MEMORY,
     CLIENT_DELTA_MEMORY,
+    CLIENT_REGISTERED,
     type MetricEvent,
     type MetricEventPayload,
     emitMetricEvent,

src/lib/metrics.ts

@@ -169,6 +169,11 @@ export function registerPrometheusMetrics(
         help: 'Number of times a feature flag has been used',
         labelNames: ['toggle', 'active', 'appName'],
     });
+    const clientRegistrationTotal = createCounter({
+        name: 'client_registration_total',
+        help: 'Number of times a an application have registered',
+        labelNames: ['appName', 'environment'],
+    });
 
     dbMetrics.registerGaugeDbMetric({
         name: 'feature_toggles_total',
@@ -807,6 +812,9 @@ export function registerPrometheusMetrics(
         clientDeltaMemory.reset();
         clientDeltaMemory.set(event.memory);
     });
+    eventBus.on(events.CLIENT_REGISTERED, ({ appName, environment }) => {
+        clientRegistrationTotal.labels({ appName, environment }).inc();
+    });
 
     events.onMetricEvent(
         eventBus,