Summary - Clustering

Combine fork, IPC and isMaster to write a cluster server.

Summary - Clustering

In this group you learned the cluster module: the master starts workers with cluster.fork(), workers share the port, and IPC carries messages. cluster.isMaster separates master from worker.

Graceful reload gives zero-downtime updates, and the exit event drives auto-restart. These patterns are the foundation of scaling Node.js servers in production.

When to use cluster

Cluster is most useful for CPU-heavy apps and HTTP servers. A single process leaves multi-core machines idle; cluster uses all cores.

For I/O-heavy workloads (network, disk) the gain is smaller, because Node.js's event loop already handles concurrency. Still, the multi-core advantage always applies.

Exercise Log master or worker

If cluster.isMaster is true log "master", otherwise log "worker".

Show example solution

const cluster = require("cluster");
console.log(cluster.isMaster ? "master" : "worker");

Test yourself

What is the main purpose of the cluster module?
- Speeding up file reads
- Using multiple CPU cores
- Rendering a web page
- Caching database queries
Show answer

Using multiple CPU cores — Cluster lets you use all CPU cores on a multi-core machine.
Match each piece to its role

cluster.fork()

Starts a worker
cluster.isMaster

Main flag
cluster.on("exit")

On worker exit
require("cluster")

Imports the module

Next lesson: worker_threads

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