feat: add prom metrics (#8980)

This PR adds prometheus metrics that allows us to see whether or not
tags and namePrefix is used at all in our cloud offering.

src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts

@@ -23,6 +23,7 @@ import type { OpenApiService } from '../../services/openapi-service';
 import { NONE } from '../../types/permissions';
 import { createResponseSchema } from '../../openapi/util/create-response-schema';
 import type { ClientFeaturesQuerySchema } from '../../openapi/spec/client-features-query-schema';
+import type EventEmitter from 'events';
 import {
     clientFeatureSchema,
     type ClientFeatureSchema,
@@ -33,6 +34,10 @@ import {
 } from '../../openapi/spec/client-features-schema';
 import type ConfigurationRevisionService from '../feature-toggle/configuration-revision-service';
 import type { ClientFeatureToggleService } from './client-feature-toggle-service';
+import {
+    CLIENT_METRICS_NAMEPREFIX,
+    CLIENT_METRICS_TAGS,
+} from '../../internals';
 
 const version = 2;
 
@@ -62,6 +67,8 @@ export default class FeatureController extends Controller {
 
     private flagResolver: IFlagResolver;
 
+    private eventBus: EventEmitter;
+
     private featuresAndSegments: (
         query: IFeatureToggleQuery,
         etag: string,
@@ -92,6 +99,7 @@ export default class FeatureController extends Controller {
         this.configurationRevisionService = configurationRevisionService;
         this.featureToggleService = featureToggleService;
         this.flagResolver = config.flagResolver;
+        this.eventBus = config.eventBus;
         this.logger = config.getLogger('client-api/feature.js');
 
         this.route({
@@ -210,6 +218,14 @@ export default class FeatureController extends Controller {
             return {};
         }
 
+        if (namePrefix) {
+            this.eventBus.emit(CLIENT_METRICS_NAMEPREFIX);
+        }
+
+        if (tag) {
+            this.eventBus.emit(CLIENT_METRICS_TAGS);
+        }
+
         const tagQuery = this.paramToArray(tag);
         const projectQuery = this.paramToArray(project);
         const query = await querySchema.validateAsync({

src/lib/metric-events.ts

@@ -1,4 +1,5 @@
 import type EventEmitter from 'events';
+import { CLIENT_METRICS } from './internals';
 
 const REQUEST_TIME = 'request_time';
 const DB_TIME = 'db_time';
@@ -14,6 +15,8 @@ const USER_LOGIN = 'user-login' as const;
 const EXCEEDS_LIMIT = 'exceeds-limit' as const;
 const REQUEST_ORIGIN = 'request_origin' as const;
 const ADDON_EVENTS_HANDLED = 'addon-event-handled' as const;
+const CLIENT_METRICS_NAMEPREFIX = 'client-api-nameprefix';
+const CLIENT_METRICS_TAGS = 'client-api-tags';
 
 type MetricEvent =
     | typeof REQUEST_TIME
@@ -28,7 +31,9 @@ type MetricEvent =
     | typeof STAGE_ENTERED
     | typeof USER_LOGIN
     | typeof EXCEEDS_LIMIT
-    | typeof REQUEST_ORIGIN;
+    | typeof REQUEST_ORIGIN
+    | typeof CLIENT_METRICS_NAMEPREFIX
+    | typeof CLIENT_METRICS_TAGS;
 
 type RequestOriginEventPayload = {
     type: 'UI' | 'API';
@@ -76,6 +81,8 @@ export {
     EXCEEDS_LIMIT,
     REQUEST_ORIGIN,
     ADDON_EVENTS_HANDLED,
+    CLIENT_METRICS_NAMEPREFIX,
+    CLIENT_METRICS_TAGS,
     type MetricEvent,
     type MetricEventPayload,
     emitMetricEvent,

src/lib/metrics.ts

@@ -504,6 +504,16 @@ export function registerPrometheusMetrics(
         })
         .set(config.rateLimiting.callSignalEndpointMaxPerSecond * 60);
 
+    const namePrefixUsed = createCounter({
+        name: 'nameprefix_count',
+        help: 'Count of nameprefix usage in client api',
+    });
+
+    const tagsUsed = createCounter({
+        name: 'tags_count',
+        help: 'Count of tags usage in client api',
+    });
+
     const featureCreatedByMigration = createCounter({
         name: 'feature_created_by_migration_count',
         help: 'Feature createdBy migration count',
@@ -734,6 +744,14 @@ export function registerPrometheusMetrics(
         mapFeaturesForClientDuration.observe(duration);
     });
 
+    eventBus.on(events.CLIENT_METRICS_NAMEPREFIX, () => {
+        namePrefixUsed.inc();
+    });
+
+    eventBus.on(events.CLIENT_METRICS_TAGS, () => {
+        tagsUsed.inc();
+    });
+
     events.onMetricEvent(
         eventBus,
         events.REQUEST_ORIGIN,