A single instance of Node runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node processes to handle the load.

NodeJs - Clustering.js

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

if (cluster.isMaster) {
	
	// Fork workers
	for (var i = 0; i < numCPUs; i++) {
		cluster.fork();
	}
	
	// Fork event of workers
	cluster.on('fork', function(worker) {
		console.log(worker.process.pid + ':is forked');
	});
	
	// Online event of workers
	cluster.on('online', function(worker) {
		console.log(worker.process.pid + ':is online');
	});
	
	// Listening event of workers
	cluster.on('listening', function(worker, address) {
		console.log(worker.process.pid + ':is listening');
	});
	
	// Exiting event of workers
	cluster.on('exit', function(worker, code, signal) {
		console.log(worker.process.pid + ':is exited');
		
		// Now fork a new worker
		cluster.fork();
	});
	
} else {
	
	// Run server for each worker
	http.createServer(function(req, res) {
		res.writeHead(200);
		res.end("Hello World\n");
	}).listen(8000);
	
	// Throw an error for test
	var randNum = Math.random() * 10000;
	setTimeout(function(){
		throw new Error('Oh no! An error!');
	}, randNum);
	
}