express-prom-bundle

What is express-prom-bundle?

The express-prom-bundle package is a middleware for Express.js that integrates Prometheus metrics collection and reporting. It allows you to easily monitor the performance and health of your Express applications by exposing various metrics that Prometheus can scrape.

What are express-prom-bundle's main functionalities?

Basic Setup

This code demonstrates the basic setup of express-prom-bundle in an Express application. It initializes the middleware and includes it in the app, which will start collecting and exposing metrics.

const express = require('express');
const promBundle = require('express-prom-bundle');

const app = express();
const metricsMiddleware = promBundle({ includeMethod: true });

app.use(metricsMiddleware);

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Custom Metrics

This code demonstrates how to create and use custom metrics with express-prom-bundle. It shows how to define a custom counter and increment it in a route handler.

const express = require('express');
const promBundle = require('express-prom-bundle');
const promClient = require('prom-client');

const app = express();
const metricsMiddleware = promBundle({ includeMethod: true });

app.use(metricsMiddleware);

const customCounter = new promClient.Counter({
  name: 'custom_counter',
  help: 'Example of a custom counter',
});

app.get('/increment', (req, res) => {
  customCounter.inc();
  res.send('Counter incremented');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Custom Metrics Endpoint

This code demonstrates how to customize the endpoint where Prometheus metrics are exposed. By setting the `metricsPath` option, you can change the default `/metrics` endpoint to a custom path.

const express = require('express');
const promBundle = require('express-prom-bundle');

const app = express();
const metricsMiddleware = promBundle({ includeMethod: true, metricsPath: '/custom-metrics' });

app.use(metricsMiddleware);

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Other packages similar to express-prom-bundle

prom-client

prom-client is a Prometheus client for Node.js that allows you to create and expose custom metrics. Unlike express-prom-bundle, it does not provide middleware for Express, so you need to manually integrate it into your application.

express-status-monitor

express-status-monitor is a simple, self-hosted module based on Socket.io and Chart.js to report realtime server metrics for Express-based applications. It provides a web-based dashboard for monitoring but does not integrate with Prometheus.

README

express prometheus bundle

Express middleware with popular prometheus metrics in one bundle. It's also compatible with koa v1 (see below).

Internally it uses prom-client. See: https://github.com/siimon/prom-client

Included metrics:

• up: normally is just 1
• http_request_duration_seconds: http latency histogram labeled with status_code, method and path

Please note version 2.x is NOT backwards compatible with 1.x

Install

npm install express-prom-bundle

Usage

const promBundle = require("express-prom-bundle");
const metricsMiddleware = promBundle({/* options */ });
const app = require("express")();

app.use(metricsMiddleware);
app.use(/* your middleware */);
app.listen(3000);

• call your endpoints
• see your metrics here: http://localhost:3000/metrics

ALERT!

The order in which the routes are registered is important, since only the routes registered after the express-prom-bundle will be measured

You can use this to your advantage to bypass some of the routes. See the example below.

Options

• buckets: buckets used for http_request_seconds histogram
• includeMethod: include HTTP method (GET, PUT, ...) as a label to http_request_duration_seconds
• includePath: include URL path as a label (see below)
• normalizePath: boolean or function(req) - path normalization for includePath option
• excludeRoutes: array of strings or regexp specifying which routes should be skipped for http_request_duration_seconds metric. It uses req.path as subject when checking
• autoregister: if /metrics endpoint should be registered. (Default: true)
• whitelist, blacklist: array of strings or regexp specifying which metrics to include/exclude

More details on includePath option

The goal is to have separate latency statistics by URL path, e.g. /my-app/user/, /products/by-category etc.

Just taking req.path as a label value won't work as IDs are often part of the URL, like /user/12352/profile. So what we actually need is a path template. The module tries to figure out what parts of the path are values or IDs, and what is an actual path. The example mentioned before would be normalized to /user/#val/profile and that will become the value for the label.

You can override this magical behavior and define your own function by providing an optional callback using normalizePath option.

For more details:

• url-value-parser - magic behind automatic path normalization
• normalizePath.js - source code for path processing, for you

express example

setup std. metrics but exclude up-metric:

"use strict";

const express = require("express");
const app = express();
const promBundle = require("express-prom-bundle");


// calls to this route will not appear in metrics
// because it's applied before promBundle
app.get("/status", (req, res) => res.send("i am healthy"));

app.use(promBundle({
    includePath: true,
    excludeRoutes: ["/foo"]
}));

// this call will NOT appear in metrics, because it matches excludeRoutes
app.get("/foo", (req, res) => res.send("bar"));

// calls to this route will appear in metrics
app.get("/hello", (req, res) => res.send("ok"));

app.listen(3000);

See an advanced example on github

koa v1 example

const promBundle = require("express-prom-bundle");
const koa = require("koa");
const c2k = require("koa-connect");
const metricsMiddleware = promBundle({/* options */ });

const app = koa();

app.use(c2k(metricsMiddleware));
app.use(/* your middleware */);
app.listen(3000);

Changelog

• 2.0.0

  • the reason for the version lift were:
    • compliance to official naming recommendation: https://prometheus.io/docs/practices/naming/
    • stopping promotion of an anti-pattern - see https://groups.google.com/d/msg/prometheus-developers/XjlOnDCK9qc/ovKzV3AIBwAJ
    • dealing with prom-client being a singleton with a built-in registry
  • main histogram metric renamed from http_request_seconds to http_request_duration_seconds
  • options removed: prefix, keepDefaultMetrics
  • factory removed (as the only reason of it was adding the prefix)
  • upgrade prom-client to 6.3.0
  • code style changed to the one closer to express

• 1.2.1

  • upgrade prom-client to 6.1.2
  • add options: includeMethod, includePath, keepDefaultMetrics

License

MIT