cluster module

Learn to use multiple cores with the cluster module.

What is the cluster module?

Node.js runs on a single thread, so it uses only one CPU core. The cluster module lets you create one master process and multiple worker processes. Each worker is a separate process and shares incoming connections.

On an 8-core machine you can run 8 workers and use all cores. cluster is a built-in Node.js module; you import it with require("cluster"). It is one of the easiest ways to boost server performance.

Master and worker processes

The cluster module has two roles. The master process starts and monitors workers; it does not handle requests itself. The worker process does the real work: listens on the server, answers requests.

The master starts workers with cluster.fork(). Because each worker is a separate process, if one crashes the others keep running. This gives you high availability.

Exercise Import cluster and log its type

Import the cluster module with require. Log typeof cluster with console.log.

Show example solution

const cluster = require("cluster");
console.log(typeof cluster);

Test yourself

How is cluster imported?
```
const cluster = require("cluster")
```
- const cluster = require("cluster")
- import cluster from "node"
- const cluster = require("http")
- const cluster = new Cluster()
Show answer

const cluster = require("cluster") — cluster is imported with require('cluster').

Complete the module name

const cluster = require("____")

Show answer

const cluster = require("cluster")

Match each piece to its role

cluster.isMaster

Main process?
cluster.fork

Starts a worker
cluster.worker

Current worker
require("cluster")

Imports the module

Next lesson: cluster.fork

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