Add node_module prom-client to synthetic-pop-javascript-playback-engine

Intro:

This idea, makes alot of sense for people that wants to use synthetic checks to query a prometheus endpoint. 

Implementation from your side is simply add the prom-client module in synthetic checks pods.

Description:

If you add the prometheus module, we will be able to use this module to query prometheus metrics and use them in the synthetic checks.

Example, collect metrics from Prometheus endpoint:

const http = require('http')

const url = require('url')

const client = require('prom-client')

// Create a Registry which registers the metrics

const register = new client.Registry()

// Add a default label which is added to all metrics

register.setDefaultLabels({

  app: 'example-nodejs-app'

})

// Enable the collection of default metrics

client.collectDefaultMetrics({ register })

// Define the HTTP server

const server = http.createServer(async (req, res) => {

  // Retrieve route from request object

  const route = url.parse(req.url).pathname

  if (route === '/metrics') {

    // Return all metrics the Prometheus exposition format

    res.setHeader('Content-Type', register.contentType)

    res.end(register.metrics())

  }

})

// Start the HTTP server which exposes the metrics on http://localhost:8080/metrics

server.listen(8080)

Then I can process the data and trigger a synthetic check when a series is not as expected.

From your side you only need to have the module available in the modules directory, to install you can simply:

npm install prom-client

cheers