app.js

const express = require('express');
const port = 3000;
const cluster = require('cluster');
const totalCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  console.log(`Number of CPUs is ${totalCPUs}`);
  console.log(`Master ${process.pid} is running`);

  // Fork workers.
  for (let i = 0; i < totalCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`);
    console.log("Let's fork another worker!");
    cluster.fork();
  });

} else {
  const app = express();
  console.log(`Worker ${process.pid} started`);

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

  app.get('/api/:n', function (req, res) {
    let n = parseInt(req.params.n);
    let count = 0;

    if (n > 5000000000) n = 5000000000;

    for(let i = 0; i <= n; i++){
      count += i;
    }

    res.send(`Final count is ${count}`);
  })

  app.listen(port, () => {
    console.log(`App listening on port ${port}`);
  })

}