LeetCode Backend System

A scalable microservices-based backend system for running and evaluating code submissions, similar to LeetCode. Built with Node.js, TypeScript, and Docker.

🏗️ Architecture

This system consists of three main microservices:

Service	Port	Description	Database
Problem Service	3001	Manages coding problems, test cases, and problem metadata	MongoDB
Submission Service	3002	Handles code submissions, user data, and submission status	MongoDB
Evaluation Service	3003	Executes code in isolated containers and evaluates results	None (stateless)

🔧 Supporting Infrastructure

• MongoDB: Primary database for problem and submission data
• Redis: Message queue and caching layer (BullMQ)
• Docker-in-Docker: Isolated code execution environment
• Winston: Structured logging with daily rotation

🚀 Features

• Multi-language Support: Execute code in JavaScript, C++, and Python
• Isolated Execution: Secure code execution using Docker containers
• Asynchronous Processing: Queue-based job processing with BullMQ
• Comprehensive Logging: Structured logging with correlation IDs
• Health Checks: Service health monitoring and dependency management
• Scalable Architecture: Designed for horizontal scaling

💻 Supported Languages

Language	Timeout	Docker Image	Description
JavaScript	10 seconds	Node.js	JavaScript/Node.js code execution
C++	10 seconds	GCC	C++ code compilation and execution
Python	40 seconds	Python 3	Python code execution

📋 Prerequisites

• Docker & Docker Compose

🛠️ Quick Start

Using Docker Compose (Recommended)

1. Clone the repository

   git clone https://github.com/Abhi-wolf/leetcode_node_backend
   cd leetcode_node_backend

2. Start all services

   # Production build
   docker-compose up -d
   
   # Development with hot reload
   docker-compose -f compose-dev.yaml up -d

3. Verify services are running

   curl http://localhost:3001/api/v1/health  # Problem Service
   curl http://localhost:3002/api/v1/health  # Submission Service
   curl http://localhost:3003/api/v1/health  # Evaluation Service

🔌 API Endpoints

Problem Service (Port 3001)

• GET /api/v1/problems/search - List all problems and search by query
• GET /api/v1/problems/:id - Get problem by ID
• POST /api/v1/problems - Create new problem
• PUT /api/v1/problems/:id - Update problem
• DELETE /api/v1/problems/:id - Delete problem
• GET /api/v1/health - Health check

Submission Service (Port 3002)

• POST /api/v1/submissions - create new submission
• GET /api/v1/submissions/:id - Get submission details
• GET /api/v1/health - Health check

Evaluation Service (Port 3003)

• GET /api/v1/health - Health check

⚙️ Configuration

Environment variables can be set in .env files or Docker Compose:

Language Configuration

Language-specific settings are configured in evaluation_service/src/config/language.config.ts:

• JavaScript: 20 second execution timeout
• C++: 10 second execution timeout
• Python: 40 second execution timeout

🔍 Monitoring & Logging

• Winston Logger: Structured logging with daily rotation
• Correlation IDs: Request tracking across services
• Health Checks: /api/v1/health endpoints
• Morgan Middleware: HTTP request logging
• Queue Monitoring: BullMQ job status and metrics

Logs

# View service logs
docker-compose logs problem-service
docker-compose logs submission-service
docker-compose logs evaluation-service

# View all logs
docker-compose logs -f