Order Execution Engine

A backend engine that processes market orders, routes them to the best Decentralized Exchange (DEX) based on price, and streams real-time updates via WebSockets.

Public Deployment & Video

• Live Demo URL: []
• Demo Video: []

Design Decisions

Order Type Strategy

I chose Market Orders to prioritize speed of execution and immediate liquidity, which is critical for a routing engine demonstration. To extend this system for Limit or Sniper orders, the worker logic would be modified to check a target price or launch time trigger before proceeding to the "Routing" phase.

Architecture

• WebSockets over HTTP: The system uses a single WebSocket connection for both order submission and status updates. This reduces network overhead and ensures the client never misses an update due to connection latency.
• Queue-Based Concurrency: BullMQ is used to decouple the API from the execution logic. This ensures the server remains responsive even under high load, processing orders at a controlled rate.
• Redis Pub/Sub: A dedicated Redis channel is created for each order ID. This allows the worker to publish updates asynchronously without blocking the main thread.

Tech Stack

• Runtime: Node.js, TypeScript
• Framework: Fastify (Chosen for high-performance WebSocket support)
• Database: PostgreSQL (Persistence), Redis (Queue & Real-time Pub/Sub)
• ORM: Prisma
• Queue: BullMQ

Local Setup Instructions

1. Prerequisites Ensure Docker and Node.js are installed.

2. Start Infrastructure Run the following command to start PostgreSQL and Redis containers:

   docker-compose up -d

3. Install Dependencies

   npm install

4. Initialize Database Generate the Prisma client and push the schema to the database:

   npx prisma generate
   npx prisma migrate dev --name init

5. Run the Server

   npm run dev

   The server will start at http://localhost:3000.

API Usage

WebSocket Endpoint

URL: ws://localhost:3000/api/orders/connect

Request Payload: Send this JSON immediately after connecting:

{
  "action": "execute_order",
  "tokenIn": "SOL",
  "tokenOut": "USDC",
  "amountIn": 5
}

Response Stream:

1. Pending: Order received and queued.
2. Routing: Comparing prices between Raydium and Meteora.
3. Building: Constructing the transaction.
4. Submitted: Transaction sent to the network.
5. Confirmed: Transaction successful (includes TX Hash).

Testing

Run the unit and integration test suite (covers routing logic and queue behavior):

npm test