Cluster Module

The cluster module is a core Node.js module that allows you to create child processes (workers) that share the same server port. It is especially useful for taking advantage of multi-core systems to handle a high number of requests more efficiently.

Why Use the Cluster Module?

Node.js is single-threaded, meaning it runs on a single core by default. This can be a limitation when you want to scale your application to handle more traffic. The cluster module helps you distribute the load across multiple cores, making your application more efficient and scalable.

Here's a basic structure of how the cluster module works:

1. Master Process: This is the main process that spawns worker processes.
2. Worker Processes: These are the child processes that handle the actual workload.

Creating the Clustered Server

Workers can share any TCP connection. Here's an example how to create a basic HTTP server.

import cluster from 'cluster';
import { cpus } from 'os';
import http from 'http';

const numCPUs = cpus().length;

// Initialize Master Process
const initMasterProcess = () => {
  console.log(`Master ${process.pid} is running`);

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

  cluster.on('exit', (worker, code, signal) => {
    console.log(`Worker ${worker.process.pid} died`);
  });
};

// Initialize Worker Process
const initWorkerProcess = () => {
  const server = http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello, world!\n');
  });

  server.listen(8000, () => {
    console.log(`Worker ${process.pid} started and listening on port 8000`);
  });
};

// Main function to start the cluster
const startCluster = () => {
  if (cluster.isMaster) {
    initMasterProcess();
  } else {
    initWorkerProcess();
  }
};

// Start the cluster
startCluster();

1. Master Process

   • The master process checks if it is the primary process.
   • It then forks (creates) a number of worker processes equal to the number of CPU cores.

2. Worker Processes

   • Each worker process runs the code inside the else block.
   • Each worker creates an HTTP server that listens on port 8000.

3. Inter-process Communication

   The master and worker processes can communicate with each other using the cluster module's messaging API, though it's not shown in this basic example.