Prometheus Node.js Example

app.js

const client = require('prom-client');
const express = require('express');
const server = express();
const register = new client.Registry();

// Probe every 5th second.
const intervalCollector = client.collectDefaultMetrics({prefix: 'node_', timeout: 5000, register});

const counter = new client.Counter({
    name: "node_my_counter",
    help: "This is my counter"
});

const gauge = new client.Gauge({
    name: "node_my_gauge",
    help: "This is my gauge"
});

const histogram = new client.Histogram({
    name: "node_my_histogram",
    help: "This is my histogram",
    buckets: [0.1, 5, 15, 50, 100, 500]
});

const summary = new client.Summary({
    name: "node_my_summary",
    help: "This is my summary",
    percentiles: [0.01, 0.05, 0.5, 0.9, 0.95, 0.99, 0.999]
});

const requestHistogram = new client.Histogram({
    name: "request_histogram",
    help: "Histogram for requests",
    labelNames: ['status_code'],
    buckets: [0.1, 5, 15, 50, 100, 500]
});

register.registerMetric(counter);
register.registerMetric(gauge);
register.registerMetric(histogram);
register.registerMetric(summary);
register.registerMetric(requestHistogram);

const rand = (low, high) => Math.random() * (high - low) + low;


setInterval(() => {
    counter.inc(rand(0, 1));

    gauge.set(rand(0, 15));

    histogram.observe(rand(0, 10));

    summary.observe(rand(0, 10));


}, 1000);


server.get('/metrics', (req, res) => {
    res.set('Content-Type', register.contentType);
    res.end(register.metrics());
});

// Middleware
function newObservableRequest(histogram, func) {
    return (req, res) => {
        let start = +new Date();
        func(req, res);
        let end = +new Date();
        let elapsed = end - start;
        let code = req.method === "GET" ? "200" : "400";
        histogram.labels(code).observe(elapsed);
    }
}

server.get('/', newObservableRequest(requestHistogram, (req, res) => {
    console.log("GET");
    res.end();
}));

server.post('/', newObservableRequest(requestHistogram, (req, res) => {
    console.log("POST");
    res.end();
}));

console.log('Server listening to 8080, metrics exposed on /metrics endpoint');
server.listen(8080);