chore: proxy repository load features metrics (#6314)

## About the changes

- Adds createHistogram
- Adds histogram metrics for proxy-repositorys loading features

src/lib/metric-events.ts

@@ -4,6 +4,7 @@ const SCHEDULER_JOB_TIME = 'scheduler_job_time';
 const FEATURES_CREATED_BY_PROCESSED = 'features_created_by_processed';
 const EVENTS_CREATED_BY_PROCESSED = 'events_created_by_processed';
 const PROXY_REPOSITORY_CREATED = 'proxy_repository_created';
+const PROXY_FEATURES_FOR_TOKEN_TIME = 'proxy_features_for_token_time';
 
 export {
     REQUEST_TIME,
@@ -12,4 +13,5 @@ export {
     FEATURES_CREATED_BY_PROCESSED,
     EVENTS_CREATED_BY_PROCESSED,
     PROXY_REPOSITORY_CREATED,
+    PROXY_FEATURES_FOR_TOKEN_TIME,
 };

src/lib/metrics.ts

@@ -25,7 +25,12 @@ import { hoursToMilliseconds, minutesToMilliseconds } from 'date-fns';
 import { InstanceStatsService } from './features/instance-stats/instance-stats-service';
 import { ValidatedClientMetrics } from './features/metrics/shared/schema';
 import { IEnvironment } from './types';
-import { createCounter, createGauge, createSummary } from './util/metrics';
+import {
+    createCounter,
+    createGauge,
+    createSummary,
+    createHistogram,
+} from './util/metrics';
 import { SchedulerService } from './services';
 
 export default class MetricsMonitor {
@@ -231,6 +236,10 @@ export default class MetricsMonitor {
             name: 'proxy_repositories_created',
             help: 'Proxy repositories created',
         });
+        const mapFeaturesForClientDuration = createHistogram({
+            name: 'map_features_for_client_duration',
+            help: 'Duration of mapFeaturesForClient function',
+        });
 
         async function collectStaticCounters() {
             try {
@@ -409,6 +418,10 @@ export default class MetricsMonitor {
             proxyRepositoriesCreated.inc();
         });
 
+        eventBus.on(events.PROXY_FEATURES_FOR_TOKEN_TIME, ({ duration }) => {
+            mapFeaturesForClientDuration.observe(duration);
+        });
+
         eventStore.on(FEATURE_CREATED, ({ featureName, project }) => {
             featureToggleUpdateTotal.increment({
                 toggle: featureName,

src/lib/proxy/proxy-repository.ts

@@ -17,8 +17,9 @@ import { Logger } from '../logger';
 import ConfigurationRevisionService, {
     UPDATE_REVISION,
 } from '../features/feature-toggle/configuration-revision-service';
+import { PROXY_FEATURES_FOR_TOKEN_TIME } from '../metric-events';
 
-type Config = Pick<IUnleashConfig, 'getLogger' | 'frontendApi'>;
+type Config = Pick<IUnleashConfig, 'getLogger' | 'frontendApi' | 'eventBus'>;
 
 type Stores = Pick<IUnleashStores, 'projectStore' | 'eventStore'>;
 
@@ -149,12 +150,16 @@ export class ProxyRepository
     }
 
     private async featuresForToken(): Promise<FeatureInterface[]> {
-        return mapFeaturesForClient(
+        const start = Date.now();
+        const mappedFeatures = await mapFeaturesForClient(
             await this.services.featureToggleServiceV2.getClientFeatures({
                 project: this.token.projects,
                 environment: this.environmentNameForToken(),
             }),
         );
+        const duration = (Date.now() - start) / 1000;
+        this.config.eventBus.emit(PROXY_FEATURES_FOR_TOKEN_TIME, { duration });
+        return mappedFeatures;
     }
 
     private async segmentsForToken(): Promise<Segment[]> {

src/lib/util/metrics/createHistogram.ts

@@ -0,0 +1,27 @@
+import {
+    Histogram as PromHistogram,
+    HistogramConfiguration,
+} from 'prom-client';
+
+export type Histogram<T extends string = string> = {
+    histogram: PromHistogram<T>;
+    labels: (labels: Record<T, string | number>) => PromHistogram.Internal<T>;
+    observe: (value: number) => void;
+};
+
+export const createHistogram = <T extends string>(
+    options: HistogramConfiguration<T>,
+): Histogram<T> => {
+    const histogram = new PromHistogram(options);
+
+    const labels = (labels: Record<T, string | number>) =>
+        histogram.labels(labels);
+
+    const observe = (value: number) => histogram.observe(value);
+
+    return {
+        histogram,
+        labels,
+        observe,
+    };
+};

src/lib/util/metrics/index.ts

@@ -1,3 +1,4 @@
 export * from './createCounter';
 export * from './createGauge';
 export * from './createSummary';
+export * from './createHistogram';

src/test/e2e/api/proxy/proxy.e2e.test.ts

@@ -915,6 +915,7 @@ test('Should sync proxy for keys on an interval', async () => {
         {
             getLogger,
             frontendApi: { refreshIntervalInMs: 5000 },
+            eventBus: <any>{ emit: jest.fn() },
         },
         db.stores,
         app.services,
@@ -946,6 +947,7 @@ test('Should change fetch interval', async () => {
         {
             getLogger,
             frontendApi: { refreshIntervalInMs: 1000 },
+            eventBus: <any>{ emit: jest.fn() },
         },
         db.stores,
         app.services,
@@ -974,6 +976,7 @@ test('Should not recursively set off timers on events', async () => {
         {
             getLogger,
             frontendApi: { refreshIntervalInMs: 5000 },
+            eventBus: <any>{ emit: jest.fn() },
         },
         db.stores,
         app.services,
@@ -1030,6 +1033,7 @@ test('should terminate data polling when stop is called', async () => {
         {
             getLogger: getDebugLogger,
             frontendApi: { refreshIntervalInMs: 1 },
+            eventBus: <any>{ emit: jest.fn() },
         },
         db.stores,
         app.services,