How do you use multiple CPU cores with Node.js's node:cluster module?

Short answer

Create child processes (Workers) that share the same server port and distribute incoming requests with Round-Robin scheduling.

Explanation

Because Node.js is single-threaded, a server with 16 cores uses only one core and wastes the other 15 unless multiple processes are started. The node:cluster module lets the primary process create child processes with cluster.fork(), pass the server socket to them, and balance the load across them. It can also restart a child process immediately if it crashes.

Code example

import cluster from "node:cluster";
import os from "node:os";
if (cluster.isPrimary) {
  const cpus = os.cpus().length;
  for (let i = 0; i < cpus; i++) cluster.fork();
} else {
  // Ordinary server code
}

Common mistakes

• Sharing memory directly between Worker processes without a distributed intermediary such as Redis or IPC messages.

Follow-up questions

• How do Worker Threads differ from Child Processes in Node.js?

Sources

• Node.js docs — Cluster