@matteodisabatino/express-prometheus-middleware

express-prometheus-middleware

Exposes Prometheus metrics for express applications. Based on @trussle/tricorder.

By default, the module exposes information about Prometheus default metrics, garbage collection metrics and the duration and the throughput of each HTTP route that has been called at least once via endpoint /metrics. However, you can customize this behaviour via options.

Since version 1.0.0 the module supports all existing Node.js versions from 6.0.0. express and prom-client are required as peer dependencies.

Since version 3.0.0 the module has got its own official Grafana dashboard. Please note that to have information about usage of CPU and RAM, node_exporter must be used in conjunction.

The module is write in TypeScript following the Google TypeScript Style Guide. If you find something not compliant with, please provide a pull request.

In general every pull request that will:

• Let the code be compliant to Google TypeScript Style Guide
• Improve performances
• Add features

are well accepted.

Available options

Options	Type	Meaning	Default value
collectDefaultMetrics	boolean | Prometheus.DefaultMetricsCollectorConfiguration	Whether or not to collect Prometheus default metrics or configuration for prom-client	true
collectGCMetrics	boolean	Whether or not to collect garbage collection metrics	true
exclude	(req: express.Request): boolean	Avoid all matching routes to expose duration and throughput information	(req) => false
excludePaths	string[]	Avoid all matching paths to expose duration and throughput information	[]
url	string	The path to which expose metrics	/metrics

Usage

Require the module, instance an object and use the handler as an express middleware.

Basic

const express = require('express')
const { ExpressPrometheusMiddleware } = require('@matteodisabatino/express-prometheus-middleware')

const app = express()
const epm = new ExpressPrometheusMiddleware()

app.use(epm.handler)

app.listen(process.env.PORT, () => {
  console.log('Server has been started')
})

Example of advanced usage

You can easily configure your Express Prometheus Middleware instance to ignore specific endpoints in your application.

const express = require('express')
const { ExpressPrometheusMiddleware } = require('@matteodisabatino/express-prometheus-middleware')

const app = express()
const epm = new ExpressPrometheusMiddleware({
  exclude: (req) => req.method === 'POST' && req.path === '/accounts'
  // This setting will prevent to generate the duration and the throughput
  // metrics for route POST /accounts
})

app.use(epm.handler)

app.listen(process.env.PORT, () => {
  console.log('Server has been started')
})

Example of usage with custom metrics reporting

It's likely that you will want to provide additional data to your Prometheus scraper and Express Prometheus Middleware does not get in your way with this:

const express = require('express')
const { ExpressPrometheusMiddleware } = require('@matteodisabatino/express-prometheus-middleware')
// npm install --save prom-client
const Prometheus = require('prom-client')

const app = express()

const gauge = new Prometheus.Gauge({
  name: `myamazingapp_interesting_datapoint`,
  help: `A very helpful but terse explanation of this metric`,
  collect () {
  // Add your own custom logic here
    this.inc();
  },
  // Or more likely
  async collect () {
    const data = SomeRepository.getSomeRecordCounts(...);
    this.set(data.total);
  }
})

app.use(epm.handler)

app.listen(process.env.PORT, () => {
  console.log('Server has been started')
})

Viewing /metrics will then display your data alongside the information provided by this library. See the Prometheus Client documentation for better examples.