When to use workers vs cluster in Node.js - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a cluster that listens on port 3000.

Node.js

const cluster = require('cluster');
const http = require('http');

if (cluster.isMaster) {
  cluster.fork();
} else {
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello from worker [1]');
  }).listen(3000);
}

Drag options to blanks, or click blank then click option'

Acluster.workerId

Bprocess.pid

Ccluster.id

Dworker.id

Attempts:

3 left

💡 Hint

Common Mistakes

Using cluster.id which does not exist

Using worker.id which is undefined in this context

The process.pid gives the unique process ID of the worker, which helps identify which worker is responding.

2fill in blank

medium

Complete the code to create a worker thread that runs a function.

Node.js

const { Worker } = require('worker_threads');

const worker = new Worker(`
  const { parentPort } = require('worker_threads');
  parentPort.postMessage('Hello from [1]');
`, { eval: true });

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Achild process

Bmain thread

Ccluster worker

Dworker thread

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing main thread with worker thread

Using cluster worker which is a different concept

The worker thread sends a message saying 'Hello from worker thread' to indicate it is running in a worker thread.

3fill in blank

hard

Fix the error in the cluster setup to properly fork workers equal to CPU cores.

Node.js

const cluster = require('cluster');
const os = require('os');

if (cluster.isMaster) {
  const cpuCount = os.[1]().length;
  for (let i = 0; i < cpuCount; i++) {
    cluster.fork();
  }
}

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Acpus

BcpuCores

CcpuCount

Dcpu

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like cpuCount or cpuCores

Trying to use a property instead of a method

The os.cpus() method returns an array of CPU cores. Its length gives the number of cores.

4fill in blank

hard

Fill both blanks to create a worker thread that sends a message back to the main thread.

Node.js

const { Worker, isMainThread, parentPort } = require('worker_threads');

if (isMainThread) {
  const worker = new Worker(__filename);
  worker.on('message', (msg) => {
    console.log('Received:', msg);
  });
} else {
  parentPort.[1]('Hello from worker');
  parentPort.[2]('close', () => process.exit());
}

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ApostMessage

Bsend

Con

Dexit

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of postMessage

Using exit instead of on for event listening

parentPort.postMessage sends a message to the main thread, and parentPort.on listens for events like exit.

5fill in blank

hard

Fill all three blanks to create a cluster that restarts a worker when it exits.

Node.js

const cluster = require('cluster');
const http = require('http');

if (cluster.isMaster) {
  cluster.fork();
  cluster.on('[1]', (worker, code, signal) => {
    console.log(`Worker [2] died. Restarting...`);
    cluster.[3]();
  });
} else {
  http.createServer((req, res) => {
    res.end('Hello from worker');
  }).listen(3000);
}

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Aexit

Bid

Cfork

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Listening for 'disconnect' instead of 'exit'

Using worker.processId instead of worker.id

Calling cluster.disconnect() instead of cluster.fork()

The cluster listens for the 'exit' event when a worker dies, logs the worker's id, and forks a new worker to replace it.