Node.js: What is the difference between worker_threads and cluster module?

worker_threads — threads within one process. cluster — separate processes.

worker_threads:

• Shared memory (SharedArrayBuffer).
• Lower overhead.
• Can share data directly.
• Used for CPU-intensive tasks.

1const { Worker, isMainThread, parentPort } = require("worker_threads");
2
3if (isMainThread) {
4    const worker = new Worker(__filename);
5    worker.on("message", (msg) => console.log(msg));
6    worker.postMessage("start");
7} else {
8    parentPort.on("message", () => {
9        parentPort.postMessage("done");
10    });
11}

cluster:

• Separate processes.
• No shared memory.
• Higher overhead.
• Used for scaling I/O across CPUs.

When to use what:

• worker_threads — CPU-bound work (image processing, crypto).
• cluster — scaling HTTP server across CPUs.