Package Exports

express-prometheus-middleware

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Readme

Express Prometheus Middleware

This is a middleware for express servers, that expose metrics for prometheus.

The metrics exposed allows to calculate common RED (Request, Error rate, Duration of requests), and USE (Utilisation, Error rate, and Saturation), metrics

Install

yarn add express-prometheus-middleware
# or
npm i --save express-prometheus-middleware

Usage

Options

Name	Description	Default
metricsPath	Url route that will expose the metrics for scraping.	`/metrics`
collectDefaultMetrics	Whether or not to collect `prom-client` default metrics. These metrics are usefull for collecting saturation metrics, for example.	`true`
requestDurationBuckets	Buckets for the request duration metrics (in milliseconds) histogram	`[0.10, 5, 15, 50, 100, 200, 300, 400, 500, 1000, 2500]`

Example

const express = require('express');
const promMid = require('express-prometheus-middleware');
const app = express();

const PORT = 9091;
app.use(promMid({
  metricsPath: '/metrics',
  collectDefaultMetrics: true,
  requestDurationBuckers: [0.1, 0.5, 1, 1.5],
}));

app.get('/hello', (req, res) => {
  console.log('GET /hello');
  const { name = 'Anon' } = req.query;
  res.json({ message: `Hello, ${name}!` });
});

app.listen(PORT, () => {
  console.log(`Example api is listening on http://localhost:${PORT}`);
});

Metrics exposed

Default metrics from prom-client
http_requests_total: Counter for total requests received, has labels route, method, status
http_requests_duration_milliseconds: - Duration of HTTP requests in milliseconds, has labels route, method, status

The labels route and status are normalized:

route: will normalize id like route params
status: will normalize to status code family groups, like 2XX or 4XX.

Example prometheus queries

TODO