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

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/

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;

If you want to have the prom-client to collect this information, you could have a look at the heap sizes collector that is part of the library.

Where this collector fetches the heap size you could instead scrape the JSON endpoint or maybe call the functionality behind the JSON endpoint directly to publish some gauges with either 0 or 1.