springboard-metrics

Expose metrics in Prometheus format on a Node.JS API with custom Express middleware.

Features

• Integration of RED (Requests, Errors, Duration) metrics
• Standard Prometheus Metrics included (https://prometheus.io/docs/instrumenting/writing_clientlibs/#standard-and-runtime-collectors)
• Node.JS specific metrics included (https://github.com/siimon/prom-client/tree/master/lib/metrics)
• User configuration by specifying user options on initialization of the middleware
• Extensibility

Dependencies

• prom-client (https://github.com/siimon/prom-client, a Prometheus client)
• response-time (https://www.npmjs.com/package/response-time, used to measure request duration)

Installation

Install the package using NPM

npm i @springtree/springboard-metrics

Using the package

Import the package

import { prometheusMiddleware } from '@springtree/springboard-metrics';

Initialize Express API

this.app = express();

Make the Express API use the middleware

this.app.use(prometheusMiddleware('API_name', 'API_version_0.1', {defaultMetricsPath: '/metrics'}));

Expose the metrics

Import prom-client

const prometheus = require('prom-client')

Make an endpoint to expose the metrics

app.get('/metrics', (async (request, response) => { response.send(await prometheus.register.metrics()); }));

Navigate to '/metrics' to see the exposed metrics in Prometheus format.

Ignoring the /metrics path

Make sure the endpoint path and the 'defaultMetricsPath' in the options are the same.

If you don't do this, the Prometheus instance that scrapes '/metrics' will count as a request.

A Prometheus instance scrapes at a set interval, this means that the metrics will increase over time without user action.

Prometheus target

The '/metrics' endpoint is also the target for a Prometheus Instance to scrape.