fix(core)!: Change last activity to use unix time (#15951)

packages/cli/BREAKING-CHANGES.md

@@ -2,6 +2,20 @@
 
 This list shows all the versions which include breaking changes and how to upgrade.
 
+## 1.98.0
+
+### What changed?
+
+The `last_activity` metric included as a part of route metrics has been changed to output a Unix time in seconds from
+the previous timestamp label approach. The labeling approach could result in high cardinality within Prometheus and
+thus result in poorer performance.
+
+### When is action necessary?
+
+If you've been ingesting route metrics from your n8n instance (version 1.81.0 and newer), you should analyze
+how the `last_activity` metric has affected your Prometheus instance and potentially clean up the old data. Future
+metrics will also be served in a different format, which needs to be taken into account.
+
 ## 1.83.0
 
 ### What changed?

packages/cli/src/metrics/__tests__/prometheus-metrics.service.test.ts

@@ -161,8 +161,7 @@ describe('PrometheusMetricsService', () => {
 
 			expect(promClient.Gauge).toHaveBeenNthCalledWith(2, {
 				name: 'n8n_last_activity',
-				help: 'last instance activity (backend request).',
-				labelNames: ['timestamp'],
+				help: 'last instance activity (backend request) in Unix time (seconds).',
 			});
 
 			expect(app.use).toHaveBeenCalledWith(

packages/cli/src/metrics/prometheus-metrics.service.ts

@@ -3,6 +3,7 @@ import { WorkflowRepository } from '@n8n/db';
 import { Service } from '@n8n/di';
 import type express from 'express';
 import promBundle from 'express-prom-bundle';
+import { DateTime } from 'luxon';
 import { InstanceSettings } from 'n8n-core';
 import { EventMessageTypeNames } from 'n8n-workflow';
 import promClient, { type Counter, type Gauge } from 'prom-client';
@@ -137,11 +138,10 @@ export class PrometheusMetricsService {
 
 		const activityGauge = new promClient.Gauge({
 			name: this.prefix + 'last_activity',
-			help: 'last instance activity (backend request).',
-			labelNames: ['timestamp'],
+			help: 'last instance activity (backend request) in Unix time (seconds).',
 		});
 
-		activityGauge.set({ timestamp: new Date().toISOString() }, 1);
+		activityGauge.set(DateTime.now().toUnixInteger());
 
 		app.use(
 			[
@@ -155,8 +155,7 @@ export class PrometheusMetricsService {
 				`/${this.globalConfig.endpoints.formTest}/`,
 			],
 			async (req, res, next) => {
-				activityGauge.reset();
-				activityGauge.set({ timestamp: new Date().toISOString() }, 1);
+				activityGauge.set(DateTime.now().toUnixInteger());
 
 				await metricsMiddleware(req, res, next);
 			},

packages/cli/test/integration/prometheus-metrics.test.ts

@@ -1,6 +1,7 @@
 import { GlobalConfig } from '@n8n/config';
 import { WorkflowRepository } from '@n8n/db';
 import { Container } from '@n8n/di';
+import { DateTime } from 'luxon';
 import { parse as semverParse } from 'semver';
 import request, { type Response } from 'supertest';
 
@@ -53,6 +54,11 @@ describe('PrometheusMetricsService', () => {
 		prometheusService.disableAllLabels();
 	});
 
+	afterEach(() => {
+		// Make sure fake timers aren't in effect after a test
+		jest.useRealTimers();
+	});
+
 	it('should return n8n version', async () => {
 		/**
 		 * Arrange
@@ -211,9 +217,11 @@ describe('PrometheusMetricsService', () => {
 		/**
 		 * Arrange
 		 */
+		const startTime = DateTime.now().toUnixInteger();
+		jest.useFakeTimers().setSystemTime(startTime * 1000);
+
 		prometheusService.enableMetric('routes');
 		await prometheusService.init(server.app);
-		await agent.get('/api/v1/workflows');
 
 		/**
 		 * Act
@@ -230,26 +238,30 @@ describe('PrometheusMetricsService', () => {
 
 		expect(lines).toContainEqual(expect.stringContaining('n8n_test_last_activity'));
 
-		const lastActivityLine = lines.find((line) =>
-			line.startsWith('n8n_test_last_activity{timestamp='),
-		);
+		const lastActivityLine = lines.find((line) => line.startsWith('n8n_test_last_activity'));
 
 		expect(lastActivityLine).toBeDefined();
-		expect(lastActivityLine?.endsWith('1')).toBe(true);
+
+		const value = lastActivityLine!.split(' ')[1];
+
+		expect(parseInt(value, 10)).toBe(startTime);
 
 		// Update last activity
+		jest.advanceTimersByTime(1000);
 		await agent.get('/api/v1/workflows');
 
 		response = await agent.get('/metrics');
 		const updatedLines = toLines(response);
 
 		const newLastActivityLine = updatedLines.find((line) =>
-			line.startsWith('n8n_test_last_activity{timestamp='),
+			line.startsWith('n8n_test_last_activity'),
 		);
 
 		expect(newLastActivityLine).toBeDefined();
-		// Timestamp label should be different
-		expect(newLastActivityLine).not.toBe(lastActivityLine);
+
+		const newValue = newLastActivityLine!.split(' ')[1];
+
+		expect(parseInt(newValue, 10)).toBe(startTime + 1);
 	});
 
 	it('should return labels in route metrics if enabled', async () => {