How cluster module works in Node.js - Practice Exercises

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a worker process dies in Node.js cluster?

Consider a Node.js cluster setup where the master forks several worker processes. What is the default behavior when one worker process unexpectedly exits?

A The master restarts the entire cluster including all workers.

B The master shuts down all other workers and exits.

C The master ignores the dead worker and does not replace it.

D The master automatically forks a new worker to replace the dead one.

💡 Hint

Think about how Node.js cluster maintains availability by managing worker processes.

By default, the cluster module listens for 'exit' events on workers. When a worker dies, the master process forks a new worker to keep the cluster size consistent.

📝 Syntax

intermediate

Identify the correct way to create a cluster master and fork workers

Which code snippet correctly creates a cluster master that forks 2 worker processes?

A

const cluster = require('cluster');
if (cluster.isWorker) {
  cluster.fork();
  cluster.fork();
} else {
  console.log('Master running');
}

B

const cluster = require('cluster');
if (cluster.isMaster) {
  cluster.fork();
  cluster.fork();
} else {
  console.log('Worker running');
}

C

const cluster = require('cluster');
if (cluster.isMaster) {
  cluster.start(2);
} else {
  console.log('Worker running');
}

D

const cluster = require('cluster');
if (cluster.isMaster) {
  cluster.createWorkers(2);
} else {
  console.log('Worker running');
}

💡 Hint

Check the official cluster API properties and methods for forking workers.

The cluster module uses cluster.isMaster to check if the current process is the master. The master forks workers using cluster.fork().

🔧 Debug

advanced

Why does this cluster code cause workers not to start?

Given the code below, why do no worker processes start? const cluster = require('cluster'); if (cluster.isMaster) { for (let i = 0; i < 2; i++) { cluster.fork; } } else { console.log('Worker started'); }

Node.js

const cluster = require('cluster');

if (cluster.isMaster) {
  for (let i = 0; i < 2; i++) {
    cluster.fork;
  }
} else {
  console.log('Worker started');
}

A cluster.isMaster is deprecated and should be replaced with cluster.isPrimary.

B The else block should be inside the for loop to start workers.

C cluster.fork is missing parentheses, so the function is not called.

D The cluster module requires an explicit call to cluster.start() to begin.

💡 Hint

Look carefully at how functions are called in JavaScript.

The code uses cluster.fork without parentheses, so it references the function but does not execute it. Workers are never created.

❓ state_output

advanced

What is the output of this cluster worker count code?

What will be printed when running this code? const cluster = require('cluster'); if (cluster.isMaster) { console.log('Master process'); cluster.fork(); cluster.fork(); console.log('Workers count:', Object.keys(cluster.workers).length); } else { console.log('Worker process'); }

Node.js

const cluster = require('cluster');

if (cluster.isMaster) {
  console.log('Master process');
  cluster.fork();
  cluster.fork();
  console.log('Workers count:', Object.keys(cluster.workers).length);
} else {
  console.log('Worker process');
}

A

Master process
Workers count: 0
Worker process
Worker process

B

Master process
Worker process
Worker process
Workers count: 2

C

Master process
Workers count: 2
Worker process
Worker process

D

Master process
Workers count: 2

💡 Hint

Consider when the workers are fully registered in the cluster.workers object.

The cluster.fork() calls are asynchronous. Immediately after calling fork twice, cluster.workers is still empty, so length is 0. Worker processes print their messages separately.

🧠 Conceptual

expert

How does Node.js cluster module distribute incoming connections?

In a Node.js cluster with multiple worker processes, how are incoming TCP connections distributed among workers by default?

A The master process uses a round-robin algorithm to distribute connections evenly to workers.

B Each worker listens on the same port independently and the OS load balances connections.

C The first worker accepts all connections until it crashes, then the next worker takes over.

D Connections are distributed randomly without any specific order or balancing.

💡 Hint

Think about how Node.js cluster manages load balancing internally.

Node.js cluster module uses a round-robin approach by default on most platforms, where the master distributes incoming connections evenly to workers to balance load.