Real-Time Notification System

A high-performance notification service built with Node.js, Express, Socket.io, and Redis. This system uses a hybrid approach of MongoDB for persistence and Redis Pub/Sub for real-time, cross-server communication.

Features

• Instant Notifications: Delivered via WebSockets for zero-latency user experience.
• Redis Pub/Sub: Ensures that notifications are delivered even if the sender and receiver are connected to different server instances (horizontal scaling).
• Smart Caching: Uses Redis to cache user notification history with a 120-second TTL.
• Recent History: Maintains a fast-access list of the 50 most recent notifications using Redis LPUSH and LTRIM.
• Data Persistence: All notifications are permanently stored in MongoDB.

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Tech Stack

• Backend: Node.js / Express
• Real-time: Socket.io
• Database: MongoDB (Mongoose)
• Caching/Messaging: Redis (ioredis)

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System Architecture

1. POST Request: A notification is sent to the API.
2. Database & Cache: The notification is saved to MongoDB, and the specific user's Redis cache is invalidated.
3. Pub/Sub: The message is published to the Redis new_notification channel.
4. WebSocket Emission: All server instances listening to that Redis channel receive the message and emit it to the specific Socket.io room (user_userId).

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Prerequisites

• Node.js installed
• A running MongoDB instance
• A Redis instance (Upstash, Redis Cloud, or Local)

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Setup & Installation

1. Clone the Repository

   git clone https://github.com/avansingh085/Notification-System.git
   cd Notification-System
   

2. Install Dependencies

   npm install

3. Environment Configuration Create a .env file in the root directory and add your credentials:

   PORT=3000
   MONGO_URI=mongodb://127.0.0.1:27017/notifications
   REDIS_URL=your_redis_connection_url

4. Run the Server

   node src/server.js