Online Course Marketplace Microservices

Project Overview

This project implements a microservice-based online course marketplace. It consists of two microservices:

1. Course Service

   • Manages course creation, pricing, inventory (available seats), and instructor ownership.
   • Supports dynamic pricing and atomic seat reservations.

2. Order Service

   • Handles student course purchases.
   • Verifies real-time price and seat availability via the Course Service.
   • Implements seat reservation → order creation → reservation confirmation workflow.

This setup ensures strong data consistency, prevents race conditions, and handles service failures gracefully.

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ERD

Key Features

• Seat Reservation System
  Ensures atomic seat deduction and prevents double bookings.

• Retry & Fallback
  Internal service-to-service API calls include retry logic for transient failures.

• Concurrency Safe
  Locking mechanisms are implemented to avoid race conditions during seat reservation.

• Reservation Expiry
  A cron job automatically releases seats if reservations are not confirmed within a defined time.

• Health Check
  Each microservice exposes a dedicated health endpoint for monitoring.

• Dockerized Architecture
  All services run in isolated Docker containers and communicate over a shared Docker network.

Technical Stack

• Node.js + Express.js for microservices
• Docker + Docker Compose for containerization and orchestration
• Axios for internal service communication
• In-memory data storage (no database required for this assignment)

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Folder Structure

course-service
├── dist/               # Compiled JavaScript output (after build)
├── node_modules/       # Project dependencies
├── src/                # Application source code
│ ├── controllers.ts    # Handles incoming API requests
│ ├── cron.ts           # Cron jobs (reservation expiry, cleanup tasks)
│ ├── routes.ts         # API route definitions
│ ├── services.ts       # Business logic (seat reservation, pricing)
│ ├── models.ts         # Data models / in-memory storage
│ ├── interface.ts      # TypeScript interfaces & types
│ └── index.ts          # Application entry point
├── .dockerignore       # Files ignored by Docker
├── .gitignore          # Files ignored by Git
├── Dockerfile          # Docker build configuration
├── package-lock.json   # Locked dependency versions
├── package.json        # Project metadata & scripts
└── tsconfig.json       # TypeScript configuration

order-service
├── dist/               # Compiled JavaScript output (after build)
├── node_modules/       # Project dependencies
├── src/                # Application source code
│ ├── controllers.ts    # Request handlers (business logic entry points)
│ ├── routes.ts         # API route definitions
│ ├── services.ts       # Core business logic & service layer
│ ├── models.ts         # Data models / schemas
│ ├── interface.ts      # TypeScript interfaces & types
│ └── index.ts          # Application entry point
├── .dockerignore       # Files ignored by Docker
├── .env                # Environment variables (local)
├── .env.example        # Example env file for setup
├── .gitignore          # Files ignored by Git
├── Dockerfile          # Docker build configuration
├── package-lock.json   # Locked dependency versions
├── package.json        # Project metadata & scripts
└── tsconfig.json       # TypeScript configuration

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Setup Instructions

1. Clone the repository

git clone https://github.com/junayednoman/microservice-assignment
cd microservice-assignment

2. Create .env file in the Order Service

COURSE_API_URL=http://course-service:5001/api/courses

3. Build and run services with Docker Compose

docker compose up -d --build

4. Stop services

docker-compose down

Microservice APIs

Course Service

Method	Endpoint	Description
POST	/api/courses	Create a new course
GET	/api/courses/:id	Get a single course
PATCH	/api/courses/:id/price	Update course price
PATCH	/api/courses/:id/reserveSeat	Reserve a seat atomically
PATCH	/api/courses/:reservationId/confirmReservation	Confirm a reservation
PATCH	/api/courses/:reservationId/cancelReservation	Cancel a reservation
GET	/api/health	Health check

Order Service

Method	Endpoint	Description
POST	/api/orders	Create a new order (handles reservation & confirmation)
GET	/api/health	Health check

How to Test

1. Start services via Docker Compose.
2. Use Postman to:

• Create courses in Course Service.
• Place orders via Order Service.

3. Test race conditions by simulating multiple users trying to reserve the last seat simultaneously.
4. Check health endpoints:

• http://localhost:5001/api/health
• http://localhost:5002/api/health

Notes

• No database is used; in-memory storage is implemented for simplicity.
• Services communicate using Docker network: COURSE_API_URL=http://course-service:5001/api/courses
• Cron jobs handle automatic expiration of reserved seats to prevent ghost reservations.

Built with ❤️ by Junayed Noman