NodeJS Observability demo

server.js

const prometheus = require('prom-client');
const winston = require('winston');
const express = require('express');

const app = express();
const port = 3000;

const logTransports = {
  console: new winston.transports.Console({ level: 'info' }),
  // Could also configure logging to a file at a different level here.
};

const logger = winston.createLogger({
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.prettyPrint()
  ),
  transports: [logTransports.console]
});

(function simulateUnicorn() {
  const salesCounter = new prometheus.Counter({
    name: 'vc_dollars_burned',
    help: 'spend money to earn money'
  });

  const salesTimer = new prometheus.Summary({
    name: 'time_between_sales',
    help: 'ring the bell'
  });

  const lossPerWidget = 3; // "growth hacking"
  const timeBetweenSalesMillis = 400;

  var measureSaleTime = salesTimer.startTimer()
  setInterval(() => {
    logger.debug("simulation tick!");

    measureSaleTime();
    salesCounter.inc(lossPerWidget);
  }, timeBetweenSalesMillis);
})()

const landingPageHits = new prometheus.Counter({
  name: 'landing_page_hits',
  help: 'number of user who hit the landing page'
});
app.get('/', (req, res) => {
  landingPageHits.inc(1);
  res.send("Hello world!");
});

// Register an endpoint that satisfies the Prometheus scrape interface.
app.get('/metrics', (req, res) => {
  res.set('Content-Type', prometheus.register.contentType)
  res.end(prometheus.register.metrics())
});

// Register two endpoints that allow us to swap the log level back and forth
// between debug and info. Note: Don't ever do stateful actions like this
// in the context of a GET request, I'm just being lazy.
//
// Trivia: Why is this a bad idea?
app.get('/logs/debug', (req, res) => {
  logTransports.console.level = 'debug';
  res.send("log level set to: debug");
});
app.get('/logs/info', (req, res) => {
  logTransports.console.level = 'info';
  res.send("log level set to: info");
});

console.log("look at this ugly unstructured log :( \n\n");
app.listen(port, () => logger.info(`Listening on port: ${port}!`));