Does Prometheus allow you to scrape JSON information from an endpoint?

Question

I am using Prometheus to instrument a Node.js application for monitoring. I am currently using the following Node.js client for instrumentation:

prom-client

I have everything configured to gather and collect default metrics from my Node.js application and the monitoring is working as expected. I want to know if it is possible for Prometheus to scrape JSON from an endpoint that my application exposes.

For example, the Node.js application has a health check endpoint (/health), that returns simple JSON data (boolean values or 0/1) about the overall health of the application as well as it's dependencies. Can I configure Prometheus and/or the prom-client to scrape the JSON from the health endpoint and then record metrics based on that information?

Answer 1

I believe you can.

The blogposts I have linked below detail how this is done using the Prometheus Python client to ingest metrics in JSON format into Prometheus.

https://www.robustperception.io/writing-a-jenkins-exporter-in-python/ https://www.robustperception.io/writing-json-exporters-in-python/

Answer 2

I was able to find a solution using the prom-client and building my own custom metric. Will provide an example below for anyone who may be interested in doing the same. Let's say that there is a health check endpoint that returns the following JSON:

{
    "app": {
        "message": "Service is up and running!",
        "success": true
    }
}

I used the package request to make a call to the endpoint, parse the data and create a gauge to reflect a value based on the health check status. Below is an example of the /metrics endpoint in JavaScript:

const express = require('express');
const router = express.Router();
const request = require('request');

// Config for health check endpoint
const healthCheckURL = 'https://SOME_ENDPOINT/health';
const zone = 'DEV';

// Initialize Prometheus
const Prometheus = require('prom-client');
const collectDefaultMetrics = Prometheus.collectDefaultMetrics;
collectDefaultMetrics({
    timeout: 5000
});

router.get('/', (req, res) => {
    res.end(Prometheus.register.metrics());
});

const serviceHealthGauge = new Prometheus.Gauge({
    name: 'service_health',
    help: 'Health of service component',
    labelNames: ['zone']
});

setInterval(() => {
    request({
            url: healthCheckURL,
            method: "GET",
        },
        function(error, response, body) {
            if (!error && response.statusCode == 200) {
                const JSONBody = JSON.parse(body);

                // check service health
                if (JSONBody.app && JSONBody.app.success) {
                    serviceHealthGauge.set({
                        zone: zone
                    }, 1);
                } else {
                    serviceHealthGauge.set({
                        zone: zone
                    }, 0);

                }
            } else {
                serviceHealthGauge.set({
                    zone: zone
                }, 0);
            }
        }   
    );
  }, 10000);

module.exports.metricNames = ['service_health'];

module.exports = router;