Scalable Real-Time Chat Application

A highly scalable real-time chat application built with Node.js WebSockets and a Redis Pub/Sub backend.

Normally, if you run multiple instances of a WebSocket server, users connected to Server A cannot talk to users on Server B. This architecture solves that problem. By using Redis as a central message broker, all server instances stay synced. A message sent anywhere is safely broadcast to everyone everywhere.

🛠️ Tech Stack

• Backend: Node.js (node:http, node:fs)
• Real-time Engine: ws (WebSockets)
• Message Broker: ioredis (Redis Pub/Sub)
• Frontend: Vanilla HTML5 & JavaScript

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🏗️ Architecture: How It Works

[ Client 1 ] <---> ( WebSocket Server :3000 ) <---
|---> [ Redis Pub/Sub Broker ] [ Client 2 ] <---> ( WebSocket Server :3001 ) <---/

The 4-Step Message Lifecycle

1. Client Sends: A user types a message in index.html and clicks send. The browser transmits this text over a persistent WebSocket connection to the specific server port they are connected to.
2. Server Publishes: That specific server receives the data buffer. It converts the data to a text string and instantly publishes it to a Redis channel named ws-messages using the redisPublish client.
3. Redis Syncs: Redis acts as the central brain. It broadcasts the new message out to every node server instance that is listening.
4. Servers Broadcast: Every active server instance detects the message via their redisSubscribe client. They immediately loop through all of their own locally connected browser clients and deliver the chat text.

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🚀 Getting Started## 1. Prerequisites

Make sure you have Node.js and Redis running locally. You can quickly spin up Redis using Docker:

docker run -d --name local-redis -p 6379:6379 redis:7

2. Installation

Clone the repository and install the dependencies:

git clone https://github.com cd Web-Sockets npm install

3. Run the Project

Start your first server instance on the default port (3000):

npm start

4. Testing Horizontal Scaling

To see the scalability in action, open a second terminal window and start another server on a different port:

• On Windows PowerShell:

$env:PORT=3001; npm start

• On Linux/macOS:

PORT=3001 npm start

Open two separate browser tabs:

• Tab 1: http://localhost:3000
• Tab 2: http://localhost:3001

Type a message in Tab 1. You will see it instantly appear in Tab 2!

If you want to keep improving this project, tell me if you want to:

• Add a Docker Compose file to launch both your servers and Redis together with one command
• Enable unique usernames so you can see who is typing each message