feat: frontend api observability

src/lib/metric-events.ts

@@ -1,6 +1,7 @@
 const REQUEST_TIME = 'request_time';
 const DB_TIME = 'db_time';
 const SCHEDULER_JOB_TIME = 'scheduler_job_time';
+const FRONTEND_API_TIME = 'frontend_api_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';
@@ -10,6 +11,7 @@ export {
     REQUEST_TIME,
     DB_TIME,
     SCHEDULER_JOB_TIME,
+    FRONTEND_API_TIME,
     FEATURES_CREATED_BY_PROCESSED,
     EVENTS_CREATED_BY_PROCESSED,
     PROXY_REPOSITORY_CREATED,

src/lib/metrics.ts

@@ -77,6 +77,14 @@ export default class MetricsMonitor {
             maxAgeSeconds: 600,
             ageBuckets: 5,
         });
+        const frontendApiEvaluationDuration = createSummary({
+            name: 'frontend_api_duration_seconds',
+            help: 'Frontend API evaluation duration time',
+            labelNames: ['action'],
+            percentiles: [0.1, 0.5, 0.9, 0.95, 0.99],
+            maxAgeSeconds: 600,
+            ageBuckets: 5,
+        });
         const dbDuration = createSummary({
             name: 'db_query_duration_seconds',
             help: 'DB query duration time',
@@ -401,6 +409,10 @@ export default class MetricsMonitor {
             schedulerDuration.labels(jobId).observe(time);
         });
 
+        eventBus.on(events.FRONTEND_API_TIME, ({ action, time }) => {
+            frontendApiEvaluationDuration.labels(action).observe(time);
+        });
+
         eventBus.on(events.EVENTS_CREATED_BY_PROCESSED, ({ updated }) => {
             eventCreatedByMigration.inc(updated);
         });

src/lib/services/proxy-service.ts

@@ -16,7 +16,8 @@ import {
 } from '../types/settings/frontend-settings';
 import { validateOrigins } from '../util';
 import { BadDataError, InvalidTokenError } from '../error';
-import { PROXY_REPOSITORY_CREATED } from '../metric-events';
+import { FRONTEND_API_TIME, PROXY_REPOSITORY_CREATED } from '../metric-events';
+import metricsHelper from '../util/metrics-helper';
 
 type Config = Pick<
     IUnleashConfig,
@@ -45,6 +46,8 @@ export class ProxyService {
 
     private readonly services: Services;
 
+    private readonly timer: Function;
+
     /**
      * This is intentionally a Promise becasue we want to be able to await
      * until the client (which might be being created by a different request) is ready
@@ -60,6 +63,10 @@ export class ProxyService {
         this.logger = config.getLogger('services/proxy-service.ts');
         this.stores = stores;
         this.services = services;
+        this.timer = (action) =>
+            metricsHelper.wrapTimer(config.eventBus, FRONTEND_API_TIME, {
+                action,
+            });
     }
 
     async getProxyFeatures(
@@ -67,11 +74,12 @@ export class ProxyService {
         context: Context,
     ): Promise<ProxyFeatureSchema[]> {
         const client = await this.clientForProxyToken(token);
+
+        const stopTimer = this.timer('evaluateEnabledFeatures');
+
         const definitions = client.getFeatureToggleDefinitions() || [];
-
         const sessionId = context.sessionId || String(Math.random());
-
-        return definitions
+        const enabledFeatures = definitions
             .filter((feature) =>
                 client.isEnabled(feature.name, { ...context, sessionId }),
             )
@@ -84,6 +92,10 @@ export class ProxyService {
                 }),
                 impressionData: Boolean(feature.impressionData),
             }));
+
+        stopTimer();
+
+        return enabledFeatures;
     }
 
     async registerProxyMetrics(