@osrs-tracker/express-metrics ·

Prometheus HTTP metrics for the Express 5 apps of OSRS Tracker, on @prometheus-io/client (the successor of prom-client). It replaces express-prom-bundle and keeps its series unchanged:

• http_request_duration_seconds: a histogram with labels status_code, method and path, and buckets 0.003, 0.03, 0.1, 0.3, 1.5, 10. A request the client closed before the response was sent gets status 499.
• up: a gauge set to 1.
• Node process metrics (event-loop lag, heap, GC, handles), unless defaultMetrics: false.

Install

npm install @osrs-tracker/express-metrics

Usage

import express from 'express';
import { metricsMiddleware } from '@osrs-tracker/express-metrics';

const app = express();
const metricsApp = express(); // served on a separate port

app.use(metricsMiddleware({ metricsApp, normalizePath: (req, res) => req.route?.path ?? 'unknown' }));

app.listen(8080);
metricsApp.listen(9100); // GET /metrics

Options: metricsPath (default /metrics), registry (default the global register, cleared first so hot reloads don't register the metrics twice) and defaultMetrics (default true). Keep normalizePath low-cardinality: route patterns, not usernames or IDs.

The package re-exports register, Registry, Counter and Gauge, so an app can add its own metrics to the same registry. Create them after metricsMiddleware, which clears the registry.