Opinions Trading Platform

A simple and scalable in-memory opinions trading platform ( like https://probo.in/ ) built with microservices architecture, enabling users to trade on predictions and opinions. The platform consists of three main services: Gateway, Engine, and WebSocket, all connected via Redis for high-performance and low-latency communication.

Architecture

Project Structure

probo/
├── gateway/          # API Gateway Service
├── engine/           # Core Business Logic Service
├── websocket/        # Real-time WebSocket Service
├── docker-compose.yml
└── README.md

The platform uses a microservices architecture with the following components:

• Gateway Service : API gateway that handles all incoming HTTP requests and forwards them to the engine via Redis queues
• Engine Service : Core business logic service that processes all trading operations, user management, and order matching
• WebSocket Service : Real-time communication service for live orderbook updates and market data streaming
• Redis: Message broker for inter-service communication using pub/sub pattern and request queues

Features

• User Management: Create users and manage their accounts
• Symbol Management: Create and manage trading symbols/stocks
• Balance Management: Handle INR and stock balance operations
• Order Management: Buy, sell, and cancel orders with real-time matching
• Real-time Updates: WebSocket connection for live orderbook updates
• Scalable Architecture: Microservices (gateway api and websocket) with Redis-based communication for easy scaling

Getting Started

Prerequisites

1. For containerized setup

   • Docker and Docker compose

2. For normal setup

   • Node.js (v14 or higher)
   • Redis server

Running with Docker (Recommended)

1. Clone the repository:

git clone "https://github.com/abhayxcode/opinion-trading.git"
cd probo

2. Start all services using Docker Compose:

docker-compose up --build

This will start:

• Redis on port 6379
• Gateway service on port 3000
• Engine service on port 8000
• WebSocket service on port 8080

Running without Docker

1. Start Redis Server

# Install Redis (macOS)
brew install redis
redis-server

# Or install Redis (Ubuntu)
sudo apt-get install redis-server
sudo systemctl start redis-server

2. Set Environment Variables

Copy .env.example and create .env files in each service directory:

3. Install Dependencies and Start Services

Terminal 1 - Gateway Service:

cd gateway
npm install
npm run dev

Terminal 2 - Engine Service:

cd engine
npm install
npm run dev

Terminal 3 - WebSocket Service:

cd websocket
npm install
npm run dev

Production Build

For production deployment:

# Build all services
cd gateway && npm run build
cd ../engine && npm run build
cd ../websocket && npm run build

# Start production servers
cd gateway && npm start
cd ../engine && npm start
cd ../websocket && npm start

API Endpoints

Base URL

• Gateway Service: http://localhost:3000

User Management

• POST /user/create/:userId - Create a new user

Symbol Management

• POST /symbol/create/:stockSymbol - Create a new trading symbol

Balance Management

• GET /balances/inr - Get all INR balances
• GET /balances/inr/:userId - Get INR balance for specific user
• GET /balances/stock - Get all stock balances
• GET /balances/stock/:userId - Get stock balance for specific user
• POST /onramp/inr - Add INR to user's account

Trading Operations

• POST /order/buy - Place a buy order
• POST /order/sell - Place a sell order
• POST /order/cancel - Cancel an existing order

Orderbook

• GET /orderbook - Get all orderbooks
• GET /orderbook/:stockSymbol - Get orderbook for specific symbol

System Operations

• POST /reset - Reset the entire in-memory database

WebSocket Endpoints

Connect to WebSocket server at: ws://localhost:8080

Subscribe to Orderbook Updates

{
  "type": "SUBSCRIBE",
  "orderbookId": "STOCK_SYMBOL"
}

Unsubscribe from Orderbook Updates

{
  "type": "UNSUBSCRIBE",
  "orderbookId": "STOCK_SYMBOL"
}

Technology Stack

• Backend: Node.js, TypeScript, Express.js
• WebSocket: ws library
• Queue and Pub/Sub: Redis
• Containerization: Docker, Docker Compose
• Development: nodemon, ts-node

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request