Master and worker processes in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Node.js cluster master process code output?

Consider this Node.js code using the cluster module. What will be printed to the console when you run it?

Node.js

import cluster from 'cluster';
import os from 'os';

if (cluster.isPrimary) {
  console.log('Master process is running');
  const worker = cluster.fork();
  worker.on('online', () => {
    console.log('Worker is online');
  });
} else {
  console.log('Worker process started');
}

A Master process is running\nWorker is online\nWorker process started

B Worker process started\nMaster process is running\nWorker is online

C Master process is running\nWorker process started\nWorker is online

D Worker is online\nMaster process is running\nWorker process started

💡 Hint

Remember that the master process runs first and forks the worker. The worker prints its message after it starts.

The master process logs first, then forks a worker. When the worker is online, the master logs 'Worker is online'. The worker then logs 'Worker process started'. The order is master log, master event log, then worker log.

📝 Syntax

intermediate

Which option correctly creates a worker process using Node.js cluster?

Select the code snippet that correctly forks a worker process using the cluster module in Node.js.

A const worker = cluster.spawn();

B const worker = cluster.fork();

C const worker = cluster.createWorker();

D const worker = cluster.newWorker();

💡 Hint

Check the official cluster module API for the method to create a worker.

The correct method to create a worker process in Node.js cluster is cluster.fork(). Other methods do not exist and will cause errors.

🔧 Debug

advanced

Why does this cluster worker never start?

Given this code, the worker process never logs 'Worker started'. What is the cause?

Node.js

import cluster from 'cluster';

if (cluster.isPrimary) {
  cluster.fork();
} else if (cluster.isWorker) {
  console.log('Worker started');
}

A The worker code runs only if 'cluster.isWorker' is true, but the correct property is 'cluster.isWorker'.

B The property 'cluster.isWorker' does not exist; it should be 'cluster.isWorkerProcess'.

C The worker code is unreachable because 'cluster.isPrimary' is always true.

D The condition should be 'if (cluster.isWorker)' instead of 'else if'.

💡 Hint

Check the cluster module properties for identifying master and worker processes.

The property to check if the process is a worker is cluster.isWorker. Using else if means if cluster.isPrimary is true, the worker code is skipped. Changing to separate if statements ensures the worker code runs in the worker process.

❓ state_output

advanced

What is the value of 'workerCount' after this code runs?

This code counts active workers. What is the value of 'workerCount' after execution?

Node.js

import cluster from 'cluster';

let workerCount = 0;

if (cluster.isPrimary) {
  cluster.fork();
  cluster.fork();
  workerCount = Object.keys(cluster.workers).length;
} else {
  // worker code
}

A 2

B 0

C 1

D undefined

💡 Hint

cluster.workers is an object with keys for each worker process.

After forking two workers, cluster.workers contains two keys. Counting keys gives 2.

🧠 Conceptual

expert

Which statement about Node.js cluster master and worker processes is true?

Select the correct statement about how master and worker processes communicate in Node.js cluster.

A Workers automatically inherit all open network connections from the master without explicit code.

B Master and workers communicate only through shared memory variables.

C Workers can send messages to the master using process.send(), and master listens with worker.on('message').

D Master and workers share the same event loop and memory space.

💡 Hint

Think about how separate processes exchange data in Node.js cluster.

Master and worker processes are separate. They communicate via IPC messages. Workers use process.send() to send messages to the master, which listens with worker.on('message'). They do not share memory or event loops.