[8.x] Register resident set size and limit bytes metrics in APM (#215458) (#215616)

# Backport

This will backport the following commits from `main` to `8.x`:
- [Register resident set size and limit bytes metrics in APM
(#215458)](https://github.com/elastic/kibana/pull/215458)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Jesus
Wahrman","email":"41008968+jesuswr@users.noreply.github.com"},"sourceCommit":{"committedDate":"2025-03-23T21:22:30Z","message":"Register
resident set size and limit bytes metrics in APM (#215458)\n\n##
Summary\n\nResolves
https://github.com/elastic/kibana-team/issues/1565\n\nRegister resident
set size and limit bytes metrics in APM.\n\n<img width=\"1614\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/d5f1caf5-da4f-4acd-a63f-2b5256a91307\"\n/>\n\n\n###
Checklist\n\nCheck the PR satisfies following conditions. \n\nReviewers
should verify this PR satisfies this list as well.\n\n- [x] [Unit or
functional\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\nwere
updated or added to match the most common scenarios\n- [x] The PR
description includes the appropriate Release Notes section,\nand the
correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)","sha":"04772fcc456aa6b03d9ecec540cc927c23c0dd9a","branchLabelMapping":{"^v9.1.0$":"main","^v8.19.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Core","release_note:skip","backport:prev-major","backport:current-major","v9.1.0"],"title":"Register
resident set size and limit bytes metrics in
APM","number":215458,"url":"https://github.com/elastic/kibana/pull/215458","mergeCommit":{"message":"Register
resident set size and limit bytes metrics in APM (#215458)\n\n##
Summary\n\nResolves
https://github.com/elastic/kibana-team/issues/1565\n\nRegister resident
set size and limit bytes metrics in APM.\n\n<img width=\"1614\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/d5f1caf5-da4f-4acd-a63f-2b5256a91307\"\n/>\n\n\n###
Checklist\n\nCheck the PR satisfies following conditions. \n\nReviewers
should verify this PR satisfies this list as well.\n\n- [x] [Unit or
functional\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\nwere
updated or added to match the most common scenarios\n- [x] The PR
description includes the appropriate Release Notes section,\nand the
correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)","sha":"04772fcc456aa6b03d9ecec540cc927c23c0dd9a"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/215458","number":215458,"mergeCommit":{"message":"Register
resident set size and limit bytes metrics in APM (#215458)\n\n##
Summary\n\nResolves
https://github.com/elastic/kibana-team/issues/1565\n\nRegister resident
set size and limit bytes metrics in APM.\n\n<img width=\"1614\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/d5f1caf5-da4f-4acd-a63f-2b5256a91307\"\n/>\n\n\n###
Checklist\n\nCheck the PR satisfies following conditions. \n\nReviewers
should verify this PR satisfies this list as well.\n\n- [x] [Unit or
functional\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\nwere
updated or added to match the most common scenarios\n- [x] The PR
description includes the appropriate Release Notes section,\nand the
correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)","sha":"04772fcc456aa6b03d9ecec540cc927c23c0dd9a"}}]}]
BACKPORT-->

Co-authored-by: Jesus Wahrman <41008968+jesuswr@users.noreply.github.com>

src/core/packages/metrics/collectors-server-internal/src/process.test.ts

@@ -10,6 +10,7 @@
 import v8, { HeapInfo } from 'v8';
 import { mockEventLoopDelayMonitor, mockEventLoopUtilizationMonitor } from './process.test.mocks';
 import { ProcessMetricsCollector } from './process';
+import apm from 'elastic-apm-node';
 
 describe('ProcessMetricsCollector', () => {
   let collector: ProcessMetricsCollector;
@@ -103,4 +104,24 @@ describe('ProcessMetricsCollector', () => {
       expect(mockEventLoopUtilizationMonitor.reset).toBeCalledTimes(1);
     });
   });
+
+  describe('register metrics in apm', () => {
+    it('calls registerMetric in the constructor', () => {
+      const apmSpy = jest.spyOn(apm, 'registerMetric');
+
+      collector.registerMetrics();
+
+      expect(apmSpy).toHaveBeenCalledTimes(2);
+      expect(apmSpy).toHaveBeenNthCalledWith(
+        1,
+        'nodejs.memory.resident_set_size.bytes',
+        expect.any(Function)
+      );
+      expect(apmSpy).toHaveBeenNthCalledWith(
+        2,
+        'nodejs.heap.size_limit.bytes',
+        expect.any(Function)
+      );
+    });
+  });
 });

src/core/packages/metrics/collectors-server-internal/src/process.ts

@@ -9,6 +9,7 @@
 
 import v8 from 'v8';
 import type { OpsProcessMetrics, MetricsCollector } from '@kbn/core-metrics-server';
+import apm from 'elastic-apm-node';
 import { EventLoopDelaysMonitor } from './event_loop_delays_monitor';
 import { EventLoopUtilizationMonitor } from './event_loop_utilization_monitor';
 
@@ -54,6 +55,14 @@ export class ProcessMetricsCollector implements MetricsCollector<OpsProcessMetri
     return [this.getCurrentPidMetrics()];
   }
 
+  public registerMetrics() {
+    apm.registerMetric('nodejs.memory.resident_set_size.bytes', () => process.memoryUsage().rss);
+    apm.registerMetric(
+      'nodejs.heap.size_limit.bytes',
+      () => v8.getHeapStatistics().heap_size_limit
+    );
+  }
+
   public reset() {
     this.eventLoopDelayMonitor.reset();
     this.eventLoopUtilizationMonitor.reset();

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

@@ -21,7 +21,13 @@ const createMock = () => {
   return mocked;
 };
 
+const createMockProcessMetricsCollector = () => ({
+  ...createMock(),
+  registerMetrics: jest.fn().mockResolvedValue({}),
+});
+
 export const collectorMock = {
   create: createMock,
   createOpsProcessMetrics: createMockOpsProcessMetrics,
+  createProcessMetricsCollector: createMockProcessMetricsCollector,
 };

src/core/packages/metrics/server-internal/src/metrics_service.test.mocks.ts

@@ -9,7 +9,10 @@
 
 import { collectorMock } from '@kbn/core-metrics-collectors-server-mocks';
 
-export const mockOpsCollector = collectorMock.create();
+export const mockOpsCollector = {
+  ...collectorMock.create(),
+  registerMetrics: jest.fn(),
+};
 
 jest.doMock('./ops_metrics_collector', () => ({
   OpsMetricsCollector: jest.fn().mockImplementation(() => mockOpsCollector),

src/core/packages/metrics/server-internal/src/metrics_service.ts

@@ -78,6 +78,8 @@ export class MetricsService
       }
     );
 
+    this.metricsCollector.registerMetrics();
+
     await this.refreshMetrics();
 
     this.collectInterval = setInterval(() => {

src/core/packages/metrics/server-internal/src/ops_metrics_collector.test.mocks.ts

@@ -10,7 +10,7 @@
 import { collectorMock } from '@kbn/core-metrics-collectors-server-mocks';
 
 export const mockOsCollector = collectorMock.create();
-export const mockProcessCollector = collectorMock.create();
+export const mockProcessCollector = collectorMock.createProcessMetricsCollector();
 export const mockServerCollector = collectorMock.create();
 export const mockEsClientCollector = collectorMock.create();
 

src/core/packages/metrics/server-internal/src/ops_metrics_collector.test.ts

@@ -80,4 +80,12 @@ describe('OpsMetricsCollector', () => {
       expect(mockServerCollector.reset).toHaveBeenCalledTimes(2);
     });
   });
+
+  describe('#registerMetrics', () => {
+    it('call registerMetrics on the underlying collectors', () => {
+      collector.registerMetrics();
+
+      expect(mockProcessCollector.registerMetrics).toHaveBeenCalledTimes(1);
+    });
+  });
 });

src/core/packages/metrics/server-internal/src/ops_metrics_collector.ts

@@ -64,6 +64,10 @@ export class OpsMetricsCollector implements MetricsCollector<OpsMetrics> {
     };
   }
 
+  public registerMetrics() {
+    this.processCollector.registerMetrics();
+  }
+
   public reset() {
     this.processCollector.reset();
     this.osCollector.reset();