How can working with multiple threads or processes be implemented in Node.js to improve performance?

In Node.js, there are several approaches to work with multiple threads or processes:

1. cluster module — allows creating multiple worker processes that can handle requests in parallel, utilizing all CPU cores. Each worker is a separate process with its own event loop.

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

if (cluster.isMaster) {
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }
} else {
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello from worker ' + process.pid);
  }).listen(8000);
}

2. Worker Threads (worker_threads) — allow creating threads within a single process that can perform CPU-intensive tasks in parallel without blocking the main event loop.

const { Worker } = require('worker_threads');

const worker = new Worker(`
  const { parentPort } = require('worker_threads');
  parentPort.postMessage('Hello from worker thread');
`, { eval: true });

worker.on('message', message => console.log(message));

3. External processes (child_process) — can launch separate processes and communicate with them via IPC.

The choice depends on the task: for server scaling, cluster is better; for computations, worker_threads.