How to integrate Prometheus with a service?

Integration of Prometheus into a service typically involves the following steps:

1. Exposing metrics: The service needs to add an endpoint (usually /metrics) that returns metrics in a format understandable by Prometheus. This often involves using Prometheus client libraries for different languages (e.g., prom-client for Node.js, prometheus-client for Python).

2. Configuring metric collection: In Prometheus, a job is added in the configuration file (prometheus.yml) with the address of your service and the path to the metrics.

3. Running Prometheus: After configuration, Prometheus periodically polls the endpoint and collects metrics.

4. Visualization and alerts: For convenience, Grafana can be used to build dashboards and set up alerts based on collected metrics.

Example of exposing metrics in Node.js using prom-client:

const client = require('prom-client');
const express = require('express');
const app = express();

const counter = new client.Counter({
  name: 'my_service_requests_total',
  help: 'Number of requests to the service'
});

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

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

app.listen(3000);

Then, add the following to prometheus.yml:

scrape_configs:
  - job_name: 'my_service'
    static_configs:
      - targets: ['localhost:3000']

This way, Prometheus will collect metrics from your service.