Node.js Cluster Module Cluster Example


A single instance of Node.js runs in a single thread. To take advantage of multi-core systems, application can be launched in a cluster of Node.js processes to handle the load.

The cluster module allows you to easily create child processes that all share server ports.

Following example create the worker child process in main process that handles the load across multiple cores.


const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length; //number of CPUS

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

  //on exit of cluster
  cluster.on('exit', (worker, code, signal) => {
      if (signal) {
        console.log(`worker was killed by signal: ${signal}`);
      } else if (code !== 0) {
        console.log(`worker exited with error code: ${code}`);
      } else {
        console.log('worker success!');
} else {
  // Workers can share any TCP connection
  // In this case it is an HTTP server
  http.createServer((req, res) => {
    res.end('hello world\n');