Setting up a Node.js Cluster

 

var cluster = require('cluster');
var numCPUs = require('os').cpus().length;

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

   Object.keys(cluster.workers).forEach(function(id) {
    console.log("I am running with ID : "+cluster.workers[id].process.pid);
  });

  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
} else {

      //Do further processing.
}

Express :

app.js

var express=require("express");
var app=express();

app.get('/',function(req,res){

          res.end("Hello world !");

});

app.listen(3000,function(){

          console.log("Running at PORT 3000");

});

cluster.js

var cluster = require('cluster');
var numCPUs = require('os').cpus().length;

if (cluster.isMaster) {

  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
} else {

    //change this line to Your Node.js app entry point.
    require("./app.js");
}

References
https://codequs.com/p/BkCZ1VMY/setting-up-a-node-js-cluster/
https://www.sitepoint.com/how-to-create-a-node-js-cluster-for-speeding-up-your-apps/
https://nodejs.org/api/cluster.html