Cluster vs reverse proxy decision in Node.js - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Node.js Cluster vs Reverse Proxy

Which statement best explains the main difference between using Node.js cluster module and a reverse proxy like Nginx for handling multiple requests?

A Cluster and reverse proxy both create multiple Node.js processes but differ in how they handle database connections.

B Cluster forwards requests to external servers, while reverse proxy creates multiple Node.js processes internally.

C Cluster creates multiple Node.js processes to use all CPU cores, while reverse proxy forwards requests to one or more servers without creating Node.js processes.

D Cluster is used only for load balancing HTTP requests, reverse proxy is used only for caching static files.

💡 Hint

Think about where the work happens: inside Node.js or outside it.

The cluster module creates multiple Node.js processes to utilize multiple CPU cores, improving concurrency within the same machine. A reverse proxy like Nginx forwards incoming requests to one or more backend servers but does not create Node.js processes itself.

❓ component_behavior

intermediate

Behavior of Node.js Cluster Module

Given the following Node.js cluster code, what will be the output when you run it on a machine with 2 CPU cores?

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

if (cluster.isPrimary) {
  const cpuCount = os.cpus().length;
  for (let i = 0; i < cpuCount; i++) {
    cluster.fork();
  }
  console.log(`Primary process started ${cpuCount} workers.`);
} else {
  console.log(`Worker process ${process.pid} started.`);
}

A

Primary process started 2 workers.
Worker process 1234 started.
Worker process 1235 started.

B

Primary process started 1 worker.
Worker process 1234 started.

C Only one line: Primary process started 2 workers.

D SyntaxError due to missing require statements.

💡 Hint

Remember that cluster.fork() creates a new worker process for each CPU core.

The primary process forks one worker per CPU core. Each worker logs its own start message. So you see one primary message and two worker messages on a 2-core machine.

❓ state_output

advanced

Load Distribution with Reverse Proxy

Consider a reverse proxy setup with Nginx forwarding requests to two Node.js servers running on ports 3000 and 3001. If Nginx uses round-robin load balancing, what will be the sequence of server ports handling 4 consecutive requests?

A 3000, 3000, 3001, 3001

B 3000, 3001, 3000, 3001

C 3001, 3000, 3001, 3000

D All requests handled by 3000

💡 Hint

Round-robin means cycling through servers one by one.

Round-robin load balancing sends each new request to the next server in the list, cycling through them evenly.

📝 Syntax

advanced

Correct Cluster Setup Syntax

Which option correctly sets up a Node.js cluster that logs worker IDs when they start?

Node.js

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

if (cluster.isPrimary) {
  const cpuCount = os.cpus().length;
  for (let i = 0; i < cpuCount; i++) {
    cluster.fork();
  }
} else {
  console.log(`Worker ${cluster.worker.id} started.`);
}

A Add parentheses after cluster.fork like cluster.fork().

B Replace cluster.isPrimary with cluster.isMaster.

C Use cluster.worker.process.id instead of cluster.worker.id.

D Correct as is.

💡 Hint

Check the current Node.js cluster API for primary process detection.

In Node.js 20+, cluster.isPrimary replaces cluster.isMaster. The code uses the correct property and syntax.

🔧 Debug

expert

Debugging Reverse Proxy Connection Issue

You have a reverse proxy (Nginx) forwarding requests to a Node.js server on port 4000. The proxy returns 502 Bad Gateway errors. Which of the following is the most likely cause?

A Node.js server is not running or not listening on port 4000.

B Node.js server is running but has a syntax error in the code.

C Nginx configuration has a syntax error unrelated to upstream settings.

D Client browser cache is outdated.

💡 Hint

502 Bad Gateway means the proxy cannot reach the backend server.

A 502 error usually means the reverse proxy cannot connect to the backend server. If the Node.js server is not running or listening on the expected port, Nginx cannot forward requests.

Practice

1. What is the main purpose of using a cluster in a Node.js application?

easy

A. To forward HTTP requests to different servers

B. To use multiple CPU cores by creating worker processes

C. To add security features like SSL termination

D. To cache static files for faster delivery

Solution

1. Step 1: Understand what a cluster does in Node.js

   A cluster creates multiple worker processes to use all CPU cores efficiently.

2. Step 2: Compare with other options

   Forwarding requests and adding security are tasks of a reverse proxy, not a cluster.

3. Final Answer:

   To use multiple CPU cores by creating worker processes -> Option B

4. Quick Check:

   Cluster = multiple CPU cores [OK]

Hint: Clusters = multiple CPU cores, reverse proxy = request forwarding [OK]

Common Mistakes:

• Confusing cluster with reverse proxy functions
• Thinking clusters handle security features
• Assuming clusters cache files

2. Which of the following is the correct way to create a cluster in Node.js?

easy

A. const cluster = require('cluster'); cluster.fork();

B. const proxy = require('proxy'); proxy.create();

C. const http = require('http'); http.listenCluster();

D. const cluster = require('cluster'); cluster.createServer();

Solution

1. Step 1: Recall Node.js cluster module usage

   The cluster module is required with require('cluster') and workers are created with cluster.fork().

2. Step 2: Check other options for correctness

   There is no proxy module by default, http.listenCluster() and cluster.createServer() are invalid methods.

3. Final Answer:

   const cluster = require('cluster'); cluster.fork(); -> Option A

4. Quick Check:

   cluster.fork() creates workers [OK]

Hint: Use cluster.fork() to create workers in Node.js [OK]

Common Mistakes:

• Using non-existent methods like cluster.createServer()
• Confusing proxy module with cluster
• Trying to call listenCluster() on http

3. Given this setup: a Node.js app uses a cluster with 4 workers and a reverse proxy in front. What is the main benefit of this combination?

medium

A. The cluster manages security, and the reverse proxy manages CPU usage

B. The cluster handles SSL termination, and the reverse proxy creates workers

C. The reverse proxy caches data, and the cluster forwards requests

D. The reverse proxy balances traffic, and the cluster uses all CPU cores

Solution

1. Step 1: Understand roles of cluster and reverse proxy

   The cluster allows Node.js to use multiple CPU cores by creating workers. The reverse proxy balances incoming traffic among servers.

2. Step 2: Eliminate incorrect roles

   SSL termination and security are usually handled by reverse proxies, not clusters. Clusters do not forward requests or cache data.

3. Final Answer:

   The reverse proxy balances traffic, and the cluster uses all CPU cores -> Option D

4. Quick Check:

   Cluster = CPU cores, Reverse proxy = traffic balance [OK]

Hint: Cluster for CPU, reverse proxy for traffic control [OK]

Common Mistakes:

• Swapping roles of cluster and reverse proxy
• Thinking cluster handles SSL or security
• Assuming reverse proxy creates workers

4. You wrote this code snippet to create a cluster but it crashes immediately:

const cluster = require('cluster');
cluster.fork();
require('http').createServer((req, res) => res.end('Hello')).listen(3000);

What is the likely cause?

medium

A. The worker process does not listen on a port

B. Missing a callback function in cluster.fork()

C. Not checking cluster.isMaster before forking

D. No error handling for server creation

Solution

1. Step 1: Analyze cluster usage

   The code calls cluster.fork() without checking if (cluster.isMaster). Both master and worker processes fork additional processes and attempt to bind to port 3000, causing port conflicts (EADDRINUSE) and crashes.

2. Step 2: Identify the problem

   The missing if (cluster.isMaster) check before forking leads to repeated forking and server creation attempts, causing the crash.

3. Final Answer:

   Not checking cluster.isMaster before forking -> Option C

4. Quick Check:

   Check cluster.isMaster before fork [OK]

Hint: Always check cluster.isMaster before forking [OK]

Common Mistakes:

• Calling cluster.fork() without isMaster check
• Assuming fork needs a callback
• Ignoring server listen port

5. You want to improve your Node.js app's performance and reliability. You decide to use both a cluster and a reverse proxy. Which setup best achieves this goal?

hard

A. Use a cluster to run multiple workers on all CPU cores, and a reverse proxy to distribute incoming requests and handle SSL

B. Use a reverse proxy to create worker processes, and a cluster to forward requests to other servers

C. Use a cluster to cache static files, and a reverse proxy to manage CPU usage

D. Use a reverse proxy to run multiple Node.js instances, and a cluster to balance traffic

Solution

1. Step 1: Identify cluster's role in performance

   Clusters run multiple worker processes to use all CPU cores, improving performance and reliability.

2. Step 2: Identify reverse proxy's role in traffic and security

   Reverse proxies distribute incoming requests, handle SSL termination, and add security features.

3. Step 3: Evaluate options

   Only Use a cluster to run multiple workers on all CPU cores, and a reverse proxy to distribute incoming requests and handle SSL correctly assigns cluster to CPU usage and reverse proxy to traffic distribution and SSL.

4. Final Answer:

   Use a cluster to run multiple workers on all CPU cores, and a reverse proxy to distribute incoming requests and handle SSL -> Option A

5. Quick Check:

   Cluster = CPU workers, Reverse proxy = traffic & SSL [OK]

Hint: Cluster for CPU workers, reverse proxy for traffic & SSL [OK]

Common Mistakes:

• Assigning reverse proxy to create workers
• Confusing caching with cluster role
• Swapping roles of cluster and reverse proxy