Introduction

In this tutorial, we'll learn about load balancing and clustering in Express.js applications. Load balancing is a technique used to distribute workloads uniformly across servers or clusters of servers to optimize resource use, maximize throughput, minimize response time, and avoid overload on any one server.

Clustering in Express.js is a module that allows you to create child processes that run simultaneously and share the same server port. It's used to increase the performance of Node.js applications and make them fail-safe.

By the end of this tutorial, you'll be able to implement load balancing and clustering in Express.js applications.

Prerequisites:
1. Basic understanding of Express.js
2. Node.js and npm installed on your machine

Step-by-Step Guide

Load Balancing

To implement load balancing, you will need a reverse proxy server. Nginx is a popular choice for this purpose.

Clustering

Node.js has a built-in module called 'cluster' that helps to create child processes which share the server port.

Code Examples

Load Balancing with Nginx

First, install Nginx on your server. On Ubuntu, you can do this with:

sudo apt-get update
sudo apt-get install nginx

Configure Nginx for load balancing by editing the Nginx configuration file:

sudo nano /etc/nginx/nginx.conf

In the http section, add the following:

http {
  upstream myapp {
    server localhost:3000;
    server localhost:3001;
  }

  server {
    listen 80;

    location / {
      proxy_pass http://myapp;
    }
  }
}

This configuration creates a load balancer that listens on port 80 and distributes incoming requests to two Express.js apps running on port 3000 and 3001.

Clustering with Express.js

Firstly, install Express.js:

npm install express

Then, create an Express app with clustering:

// Load cluster module
const cluster = require('cluster');
// Load built-in OS module
const os = require('os');
// Load express module
const express = require('express');

if (cluster.isMaster) {
  // Create a worker for each CPU
  for (let i=0; i<os.cpus().length; i++) {
    cluster.fork();
  }
} else {
  // Workers share the TCP connection in this server
  const app = express();

  app.get('/', (req, res) => {
    res.send('Hello from Worker ' + cluster.worker.id);
  });

  app.listen(3000);
}

When you run this code, it will create an Express.js app for each CPU core on your machine. All apps will listen on port 3000, and incoming requests will be load balanced across all apps.

Summary

We've learned how to implement load balancing with Nginx and clustering with the built-in cluster module in Node.js. These techniques can help to maximize the performance of your Express.js applications.

Practice Exercises

1. Create an Express.js app that uses clustering and responds with the worker id when visited at the '/' route.

2. Configure Nginx to load balance requests to two Express.js apps running on different ports.

3. Modify the Nginx configuration to use a least connections load balancing method instead of the default round-robin method.

Additional resources

• Express.js Documentation
• Nginx Documentation
• Node.js Cluster Documentation