cluster.js

const cluster = require("cluster");
const express = require("express");
const numCPUs = require("os").cpus().length;
const app = require
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`);
  });
} else {
  // Workers can share any TCP connection
    const express = require("express");
	const app = express();
	const port = 3000;

	app.get("/slow", (req, res) => {
		var waitTill = new Date(new Date().getTime() + 5 * 1000);
		while (waitTill > new Date()) {}
		res.send("i am slow");
	  });

	app.get("/fast", (req, res) => {  
	  res.send("i am fast");
	});

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

}

express.app.js

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

app.get("/slow", (req, res) => {
    var waitTill = new Date(new Date().getTime() + 5 * 1000);
    while (waitTill > new Date()) {}
    res.send("i am slow");
  });

app.get("/fast", (req, res) => {  
  res.send("i am fast");
});

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