Scalable Chat App with Redis Pub/Sub and Socket.IO

This project is a scalable chat application built with Redis Pub/Sub and Socket.IO. It addresses the challenge of scaling real-time communication by enabling multiple servers to share messages seamlessly using Redis as a message broker.

Problem Statement

In a typical chat application:

1. Single Server Scenario:

   • Users connect to a single server.
   • Messages are exchanged effortlessly.

2. Multi-Server Scenario:

   • When the user base grows, new servers are added to distribute the load.
   • Users connected to different servers cannot communicate, breaking the real-time chat experience.

The Challenge:

How can users on different servers exchange messages seamlessly?

Solution: Redis Pub/Sub Architecture

To solve this, we introduce Redis Pub/Sub as a message broker:

• Redis Pub/Sub allows servers to publish and subscribe to messages on specific channels.
• Each chat server subscribes to a common Redis channel.
• When a user sends a message:
  1. The server publishes the message to the Redis channel.
  2. Redis broadcasts the message to all subscribed servers.
  3. Each server relays the message to its connected users.

Key Components

1. Socket.IO:

   • Enables real-time, bi-directional communication between the server and clients.

2. Redis Pub/Sub:

   • Acts as a message broker to sync messages across multiple servers.

3. Server Instances:

   • Multiple server instances can handle different users but remain in sync through Redis.

How It Works

1. User sends a message:

   • The connected server publishes the message to a Redis channel.

2. Redis distributes the message:

   • All subscribed servers receive the message.

3. Server broadcasts to clients:

   • Each server broadcasts the received message to its connected users via Socket.IO.

Example Flow

1. User 1 connects to Server 1 and sends a message: "Hello!"
2. User 4 connects to Server 2.
3. Server 1 publishes the message "Hello!" to the Redis channel.
4. Server 2 receives the message from Redis and broadcasts it to User 4.
5. Both User 1 and User 4 see the message "Hello!" in real-time.

Benefits

• Scalability:

  • Add more servers as user traffic grows.

• Seamless Communication:

  • Users on different servers can communicate without issue.

• Fault Tolerance:

  • If one server fails, others continue operating independently.

Getting Started

Prerequisites

• Node.js
• Redis