Scaling Node.js with the Cluster Module

A single instance of Node.js runs in a single thread. To take advantage of multi-core systems, you can use the built-in `cluster` module to create child processes that share the same server port, effectively multiplying the server's capacity.

How It Works

The cluster module allows you to create a master process that forks a number of worker processes. The master process doesn't handle application logic itself; it manages the workers. Incoming connections are distributed among the worker processes.

Example Implementation

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

if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);

  // Fork workers for each CPU core
  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
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello from worker\n');
  }).listen(8000);

  console.log(`Worker ${process.pid} started`);
}