Node.js Cluster With Express.js. More @ http://niralar.com/nodejs-cluster-with-expressjs/

app.js

const express = require('express');
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {

  console.log(`Master ${process.pid} is running`);

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

  cluster.on('exit', (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`);
    cluster.fork(); // Create a New Worker, If Worker is Dead
  });

} else {

  const app = express();

  app.get('/', (req, res) => res.send('Hello World!' + cluster.worker.id));

  http.createServer(app).listen(3000, function () {
    console.log("Express server listening on port 3000 as Worker " + cluster.worker.id + " running @ process " + cluster.worker.process.pid + "!");
  });

}