Improve node.js app performance using Clustering

node_cluster.js

var cluster = require('cluster');
var numCPUs = require('os').cpus().length;
var express = require("express");
var app = express();
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 {
  app.get('/', function (req, res) {
    res.end("Hello world from " + process.pid);
  });
  app.listen(3000, function () {
    console.log(process.pid, " is running at PORT 3000");
  });
}