What is the role of ’cluster’ module in Node.js, and why is it used?

The ‘cluster‘ module in Node.js is used to enable an application to run across multiple CPU cores on a single server, thus improving performance and resource utilization. It essentially creates multiple instances (workers) of the Node.js application, each of which can run on a separate CPU core. This allows for efficient load balancing and parallel processing of incoming requests, leading to better throughput and reducing the risk of bottlenecks.

Node.js is single-threaded by default, which means it can utilize only one CPU core at a time. While this is suitable for handling I/O-bound tasks, CPU-bound tasks can lead to performance degradation. By using the ‘cluster‘ module, the application can take advantage of all available CPU cores and handle a larger number of simultaneous connections.

Here’s an example of how to use the cluster module:

const cluster = require('cluster'); // Require cluster module
const http = require('http');
const numCPUs = require('os').cpus().length; // Get number of CPU cores

if (cluster.isMaster) {
  // This is the master process
  console.log(`Master process with id ${process.pid} is running`);

  // Fork a worker for each CPU core
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  // Listen for workers to be online
  cluster.on('online', (worker) => {
    console.log(`Worker ${worker.process.pid} is online`);
  });

  // Listen for workers to exit
  cluster.on('exit', (worker, code, signal) => {
    console.log(`Worker ${worker.process.pid} exited with code ${code} and signal ${signal}`);
    console.log('Starting a new worker');
    cluster.fork(); // Replace the dead worker
  });

} else {
  // This is a worker process
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello from worker!');
  }).listen(8000);

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

In this example, the ‘cluster‘ module is used to create a simple HTTP server. First, we check if this process is the master process. If it is, we fork a worker for each CPU core available. We also listen for ’online’ and ’exit’ events to track when a worker is online or when it exits, respectively. If a worker exits, we fork a new one to ensure maximum utilization of CPU cores.

If the process is not the master, it means we are in a worker process. In this case, we create an HTTP server, which listens on port 8000. Each worker process handles incoming requests independently and runs on a separate CPU core, making efficient use of available resources.