Node.js simple middleware to expose Prometheus metrics

Purpose

Module to create an HTTP server to expose Prometheus metrics.
By default it:

• runs an HTTP server to expose metrics
• instantiates and returns a prom-client
• patches http server to get request response time
• allows to define custom metrics through prom-client

Compatibility

Supported and tested : >= 14.0

Version	Supported	Tested
16.x	yes	yes
18.x	yes	yes
20.x	yes	yes

It works with different HTTP servers:

• default Node.js HTTP server
• express
• fastify

By default you can access your metrics on this endpoint: http://localhost:9350/metrics

In order to handle remote attack and to avoid high cardinality, the default behavior of this lib is to override the path label in case of HTTP code 404.

Installation

$ npm install prometheus-middleware --save

Usage

Basic

const APM = require('prometheus-middleware')
const apm = new APM()
apm.init()

Add a custom metric

const APM = require('prometheus-middleware')
const apm = new APM()
apm.init()
// ----------------
const counter = new apm.client.Counter({
  name: 'metric_name',
  help: 'metric_help',
})
// ----------------
counter.inc(); // Increment by 1
counter.inc(10); // Increment by 10

The metrics system is exactly the same as in prom-client librairy.

Configuration

The config is an JSON object which accepts the following property:

const APM = require('prometheus-middleware')
const apm = new APM({
  METRICS_ROUTE: "/metrics",
  PORT: 9350,
  PROM_CLIENT_CONF: {},
  HTTP_DURATION_BUCKETS: [0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2]
  HTTP_SUMMARY_PERCENTILES: [0.5, 0.9, 0.95, 0.99]
  NORMALIZE_ENDPOINT: false,
})
apm.init()

Destroy the APM

If you use a graceful exit method or if you want to simply stop the APM, you should run:

const APM = require('prometheus-middleware')
const apm = new APM()
apm.init()

process.on('SIGTERM', () => {
  apm.destroy()
})

Property	Default	Description
METRICS_ROUTE	/metrics	Route to expose the metrics
PORT	9350	Port to listen metrics
PROM_CLIENT_CONF	{}	Configuration of the prom-client lib
HTTP_DURATION_BUCKETS	[0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2]	List of values for HTTP request duration
HTTP_SUMMARY_PERCENTILES	[0.5, 0.9, 0.95, 0.99]	List of values for HTTP request percentiles
NORMALIZE_ENDPOINT	true	Normalize endpoint by occulting ids, and query parameters

To see how to use the module you can refer to the example folder.

Debug

The agent use debug module in order not to pollute your logs. If you want to see all agent output just use DEBUG environment variable:

DEBUG=prometheus-middleware* node myApp.js

Test

$ npm test

Coverage report can be found in coverage/.