Reset the metrics after each emission

src/core/server/metrics/collectors/mocks.ts

@@ -0,0 +1,35 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { MetricsCollector } from './types';
+
+const createMock = () => {
+  const mocked: jest.Mocked<MetricsCollector<any>> = {
+    collect: jest.fn(),
+    reset: jest.fn(),
+  };
+
+  mocked.collect.mockResolvedValue({});
+
+  return mocked;
+};
+
+export const collectorMock = {
+  create: createMock,
+};

src/core/server/metrics/collectors/os.ts

@@ -57,4 +57,6 @@ export class OsMetricsCollector implements MetricsCollector<OpsOsMetrics> {
 
     return metrics;
   }
+
+  public reset() {}
 }

src/core/server/metrics/collectors/process.ts

@@ -40,6 +40,8 @@ export class ProcessMetricsCollector implements MetricsCollector<OpsProcessMetri
       uptime_in_millis: process.uptime() * 1000,
     };
   }
+
+  public reset() {}
 }
 
 const getEventLoopDelay = (): Promise<number> => {

src/core/server/metrics/collectors/server.ts

@@ -26,12 +26,12 @@ interface ServerResponseTime {
 }
 
 export class ServerMetricsCollector implements MetricsCollector<OpsServerMetrics> {
-  private readonly requests: OpsServerMetrics['requests'] = {
+  private requests: OpsServerMetrics['requests'] = {
     disconnects: 0,
     total: 0,
     statusCodes: {},
   };
-  private readonly responseTimes: ServerResponseTime = {
+  private responseTimes: ServerResponseTime = {
     count: 0,
     total: 0,
     max: 0,
@@ -77,4 +77,17 @@ export class ServerMetricsCollector implements MetricsCollector<OpsServerMetrics
       concurrent_connections: connections,
     };
   }
+
+  public reset() {
+    this.requests = {
+      disconnects: 0,
+      total: 0,
+      statusCodes: {},
+    };
+    this.responseTimes = {
+      count: 0,
+      total: 0,
+      max: 0,
+    };
+  }
 }

src/core/server/metrics/collectors/types.ts

@@ -19,7 +19,10 @@
 
 /** Base interface for all metrics gatherers */
 export interface MetricsCollector<T> {
+  /** collect the data currently gathered by the collector */
   collect(): Promise<T>;
+  /** reset the internal state of the collector */
+  reset(): void;
 }
 
 /**

src/core/server/metrics/integration_tests/server_collector.test.ts

@@ -200,4 +200,80 @@ describe('ServerMetricsCollector', () => {
     metrics = await collector.collect();
     expect(metrics.concurrent_connections).toEqual(0);
   });
+
+  describe('#reset', () => {
+    it('reset the requests state', async () => {
+      router.get({ path: '/', validate: false }, async (ctx, req, res) => {
+        return res.ok({ body: '' });
+      });
+      await server.start();
+
+      await sendGet('/');
+      await sendGet('/');
+      await sendGet('/not-found');
+
+      let metrics = await collector.collect();
+
+      expect(metrics.requests).toEqual({
+        total: 3,
+        disconnects: 0,
+        statusCodes: {
+          '200': 2,
+          '404': 1,
+        },
+      });
+
+      collector.reset();
+      metrics = await collector.collect();
+
+      expect(metrics.requests).toEqual({
+        total: 0,
+        disconnects: 0,
+        statusCodes: {},
+      });
+
+      await sendGet('/');
+      await sendGet('/not-found');
+
+      metrics = await collector.collect();
+
+      expect(metrics.requests).toEqual({
+        total: 2,
+        disconnects: 0,
+        statusCodes: {
+          '200': 1,
+          '404': 1,
+        },
+      });
+    });
+
+    it('resets the response times', async () => {
+      router.get({ path: '/no-delay', validate: false }, async (ctx, req, res) => {
+        return res.ok({ body: '' });
+      });
+      router.get({ path: '/500-ms', validate: false }, async (ctx, req, res) => {
+        await delay(500);
+        return res.ok({ body: '' });
+      });
+
+      await server.start();
+
+      await Promise.all([sendGet('/no-delay'), sendGet('/500-ms')]);
+      let metrics = await collector.collect();
+
+      expect(metrics.response_times.avg_in_millis).toBeGreaterThanOrEqual(250);
+      expect(metrics.response_times.max_in_millis).toBeGreaterThanOrEqual(500);
+
+      collector.reset();
+      metrics = await collector.collect();
+      expect(metrics.response_times.avg_in_millis).toBe(0);
+      expect(metrics.response_times.max_in_millis).toBeGreaterThanOrEqual(0);
+
+      await Promise.all([sendGet('/500-ms'), sendGet('/500-ms')]);
+      metrics = await collector.collect();
+
+      expect(metrics.response_times.avg_in_millis).toBeGreaterThanOrEqual(500);
+      expect(metrics.response_times.max_in_millis).toBeGreaterThanOrEqual(500);
+    });
+  });
 });

src/core/server/metrics/metrics_service.test.mocks.ts

@@ -17,9 +17,10 @@
  * under the License.
  */
 
-export const mockOpsCollector = {
-  collect: jest.fn(),
-};
+import { collectorMock } from './collectors/mocks';
+
+export const mockOpsCollector = collectorMock.create();
+
 jest.doMock('./ops_metrics_collector', () => ({
   OpsMetricsCollector: jest.fn().mockImplementation(() => mockOpsCollector),
 }));

src/core/server/metrics/metrics_service.test.ts

@@ -57,37 +57,50 @@ describe('MetricsService', () => {
       expect(setInterval).toHaveBeenCalledWith(expect.any(Function), testInterval);
     });
 
-    it('emits the metrics at start', async () => {
+    it('collects the metrics at every interval', async () => {
       mockOpsCollector.collect.mockResolvedValue(dummyMetrics);
 
-      const { getOpsMetrics$ } = await metricsService.setup({
-        http: httpMock,
-      });
-
+      await metricsService.setup({ http: httpMock });
       await metricsService.start();
 
       expect(mockOpsCollector.collect).toHaveBeenCalledTimes(1);
-      expect(
-        await getOpsMetrics$()
-          .pipe(take(1))
-          .toPromise()
-      ).toEqual(dummyMetrics);
+
+      jest.advanceTimersByTime(testInterval);
+      expect(mockOpsCollector.collect).toHaveBeenCalledTimes(2);
+
+      jest.advanceTimersByTime(testInterval);
+      expect(mockOpsCollector.collect).toHaveBeenCalledTimes(3);
     });
 
-    it('collects the metrics at every interval', async () => {
+    it('resets the collector after each collection', async () => {
       mockOpsCollector.collect.mockResolvedValue(dummyMetrics);
 
-      await metricsService.setup({ http: httpMock });
-
+      const { getOpsMetrics$ } = await metricsService.setup({ http: httpMock });
       await metricsService.start();
 
+      // `advanceTimersByTime` only ensure the interval handler is executed
+      // however the `reset` call is executed after the async call to `collect`
+      // meaning that we are going to miss the call if we don't wait for the
+      // actual observable emission that is performed after
+      const waitForNextEmission = () =>
+        getOpsMetrics$()
+          .pipe(take(1))
+          .toPromise();
+
       expect(mockOpsCollector.collect).toHaveBeenCalledTimes(1);
+      expect(mockOpsCollector.reset).toHaveBeenCalledTimes(1);
 
+      let nextEmission = waitForNextEmission();
       jest.advanceTimersByTime(testInterval);
+      await nextEmission;
       expect(mockOpsCollector.collect).toHaveBeenCalledTimes(2);
+      expect(mockOpsCollector.reset).toHaveBeenCalledTimes(2);
 
+      nextEmission = waitForNextEmission();
       jest.advanceTimersByTime(testInterval);
+      await nextEmission;
       expect(mockOpsCollector.collect).toHaveBeenCalledTimes(3);
+      expect(mockOpsCollector.reset).toHaveBeenCalledTimes(3);
     });
 
     it('throws when called before setup', async () => {

src/core/server/metrics/metrics_service.ts

@@ -17,8 +17,8 @@
  * under the License.
  */
 
-import { ReplaySubject } from 'rxjs';
-import { first, shareReplay } from 'rxjs/operators';
+import { Subject } from 'rxjs';
+import { first } from 'rxjs/operators';
 import { CoreService } from '../../types';
 import { CoreContext } from '../core_context';
 import { Logger } from '../logging';
@@ -37,7 +37,7 @@ export class MetricsService
   private readonly logger: Logger;
   private metricsCollector?: OpsMetricsCollector;
   private collectInterval?: NodeJS.Timeout;
-  private metrics$ = new ReplaySubject<OpsMetrics>(1);
+  private metrics$ = new Subject<OpsMetrics>();
 
   constructor(private readonly coreContext: CoreContext) {
     this.logger = coreContext.logger.get('metrics');
@@ -46,7 +46,7 @@ export class MetricsService
   public async setup({ http }: MetricsServiceSetupDeps): Promise<InternalMetricsServiceSetup> {
     this.metricsCollector = new OpsMetricsCollector(http.server);
 
-    const metricsObservable = this.metrics$.pipe(shareReplay(1));
+    const metricsObservable = this.metrics$.asObservable();
 
     return {
       getOpsMetrics$: () => metricsObservable,
@@ -74,6 +74,7 @@ export class MetricsService
   private async refreshMetrics() {
     this.logger.debug('Refreshing metrics');
     const metrics = await this.metricsCollector!.collect();
+    this.metricsCollector!.reset();
     this.metrics$.next(metrics);
   }
 

src/core/server/metrics/ops_metrics_collector.test.mocks.ts

@@ -17,23 +17,19 @@
  * under the License.
  */
 
-export const mockOsCollector = {
-  collect: jest.fn(),
-};
+import { collectorMock } from './collectors/mocks';
+
+export const mockOsCollector = collectorMock.create();
 jest.doMock('./collectors/os', () => ({
   OsMetricsCollector: jest.fn().mockImplementation(() => mockOsCollector),
 }));
 
-export const mockProcessCollector = {
-  collect: jest.fn(),
-};
+export const mockProcessCollector = collectorMock.create();
 jest.doMock('./collectors/process', () => ({
   ProcessMetricsCollector: jest.fn().mockImplementation(() => mockProcessCollector),
 }));
 
-export const mockServerCollector = {
-  collect: jest.fn(),
-};
+export const mockServerCollector = collectorMock.create();
 jest.doMock('./collectors/server', () => ({
   ServerMetricsCollector: jest.fn().mockImplementation(() => mockServerCollector),
 }));

src/core/server/metrics/ops_metrics_collector.test.ts

@@ -35,25 +35,43 @@ describe('OpsMetricsCollector', () => {
     mockOsCollector.collect.mockResolvedValue('osMetrics');
   });
 
-  it('gathers metrics from the underlying collectors', async () => {
-    mockOsCollector.collect.mockResolvedValue('osMetrics');
-    mockProcessCollector.collect.mockResolvedValue('processMetrics');
-    mockServerCollector.collect.mockResolvedValue({
-      requests: 'serverRequestsMetrics',
-      response_times: 'serverTimingMetrics',
+  describe('#collect', () => {
+    it('gathers metrics from the underlying collectors', async () => {
+      mockOsCollector.collect.mockResolvedValue('osMetrics');
+      mockProcessCollector.collect.mockResolvedValue('processMetrics');
+      mockServerCollector.collect.mockResolvedValue({
+        requests: 'serverRequestsMetrics',
+        response_times: 'serverTimingMetrics',
+      });
+
+      const metrics = await collector.collect();
+
+      expect(mockOsCollector.collect).toHaveBeenCalledTimes(1);
+      expect(mockProcessCollector.collect).toHaveBeenCalledTimes(1);
+      expect(mockServerCollector.collect).toHaveBeenCalledTimes(1);
+
+      expect(metrics).toEqual({
+        process: 'processMetrics',
+        os: 'osMetrics',
+        requests: 'serverRequestsMetrics',
+        response_times: 'serverTimingMetrics',
+      });
     });
+  });
+
+  describe('#reset', () => {
+    it('call reset on the underlying collectors', () => {
+      collector.reset();
 
-    const metrics = await collector.collect();
+      expect(mockOsCollector.reset).toHaveBeenCalledTimes(1);
+      expect(mockProcessCollector.reset).toHaveBeenCalledTimes(1);
+      expect(mockServerCollector.reset).toHaveBeenCalledTimes(1);
 
-    expect(mockOsCollector.collect).toHaveBeenCalledTimes(1);
-    expect(mockProcessCollector.collect).toHaveBeenCalledTimes(1);
-    expect(mockServerCollector.collect).toHaveBeenCalledTimes(1);
+      collector.reset();
 
-    expect(metrics).toEqual({
-      process: 'processMetrics',
-      os: 'osMetrics',
-      requests: 'serverRequestsMetrics',
-      response_times: 'serverTimingMetrics',
+      expect(mockOsCollector.reset).toHaveBeenCalledTimes(2);
+      expect(mockProcessCollector.reset).toHaveBeenCalledTimes(2);
+      expect(mockServerCollector.reset).toHaveBeenCalledTimes(2);
     });
   });
 });

src/core/server/metrics/ops_metrics_collector.ts

@@ -49,4 +49,10 @@ export class OpsMetricsCollector implements MetricsCollector<OpsMetrics> {
       ...server,
     };
   }
+
+  public reset() {
+    this.processCollector.reset();
+    this.osCollector.reset();
+    this.serverCollector.reset();
+  }
 }