🛒 NodeJS Microservices: Order & Inventory System

A modular, production-ready microservices system inspired by e-commerce architectures, built with TypeScript, Node.js, NestJS, ExpressJS, PostgreSQL, MongoDB, Docker, and RabbitMQ/NATS for event-driven communication.

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✨ Overview

This project demonstrates a modern microservices architecture for an Order & Inventory System, suitable for real-world companies. Each service is designed with single responsibility, clear separation, and scalable technologies.

• Tech Focus: TypeScript-first, RESTful APIs, event-driven messaging, containerized infrastructure
• Monorepo: All services managed together for easy orchestration and development
• Best Practices: Security, scalability, and maintainability in mind

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🏗️ Architecture

graph TB
    %% Application Layer
    subgraph "Application Layer"
        agw[API Gateway]
        us[User Service<br/>NestJS]
        ps[Product Service<br/>ExpressJS]
        os[Order Service<br/>NestJS]
        isvc[Inventory Service<br/>ExpressJS]
        ns[Notification Service<br/>ExpressJS]
    end

    %% Database Layer
    subgraph "Database Layer"
        pg[(PostgreSQL)]
        mongo[(MongoDB)]
    end

    %% Messaging Layer
    subgraph "Messaging"
        rmq[[RabbitMQ<br/>Message Broker]]
    end

    %% Dependencies and Connections
    agw -->|REST| us
    agw -->|REST| ps
    agw -->|REST| os
    agw -->|REST| isvc
    agw -->|REST| ns

    us -- "DATABASE_URL" --> pg
    os -- "DATABASE_URL" --> pg
    ps -- "mongodb://..." --> mongo
    isvc -- "mongodb://..." --> mongo
    ns -- "mongodb://..." --> mongo

    us -- "RABBITMQ_URL" --> rmq
    os -- "RABBITMQ_URL" --> rmq
    isvc -- "RABBITMQ_URL" --> rmq
    ns -- "RABBITMQ_URL" --> rmq

    %% Messaging Events
    rmq -- "Events" --> os
    rmq -- "Events" --> isvc
    rmq -- "Events" --> ns

    %% External Ports Exposure
    agw -->|":3000"| extgw[External Access]
    us -->|":3001"| extus[External Access]
    ps -->|":3002"| extps[External Access]
    os -->|":3003"| extos[External Access]
    isvc -->|":3004"| extis[External Access]
    ns -->|":3005"| extns[External Access]
    pg -->|":9091"| extpg[External Access]
    mongo -->|":9092"| extmongo[External Access]
    rmq -->|":9093/9094"| extrmq[External Access]

    %% Class Styling
    classDef app fill:#2ecc71,stroke:#27ae60,color:white
    classDef db fill:#3498db,stroke:#2980b9,color:white
    classDef msg fill:#e67e22,stroke:#d35400,color:white
    classDef ext fill:#95a5a6,stroke:#7f8c8d,color:white

    class agw,us,ps,os,isvc,ns app
    class pg,mongo db
    class rmq msg
    class extgw,extus,extps,extos,extis,extns,extpg,extmongo,extrmq ext

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Microservice	Tech Stack	DB	Responsibility
User Service	NestJS	PostgreSQL	User registration, login, authentication, roles
Product Service	ExpressJS	MongoDB	Product CRUD (create, update, list, delete)
Order Service	NestJS	PostgreSQL	Order creation, validation, and processing
Inventory Service	ExpressJS	MongoDB	Stock tracking, update on orders
Notification Service	ExpressJS	MongoDB	Email/log notifications on events
API Gateway	ExpressJS/NestJS	-	Unified API entry, routing, token verification
Message Broker	RabbitMQ/NATS	-	Inter-service event bus

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📁 Project Structure

nodejs-microservices/
├── api-gateway/              # API Gateway (routing, auth)
├── user-service/             # User microservice
├── product-service/          # Product microservice
├── order-service/            # Order microservice
├── inventory-service/        # Inventory microservice
├── notification-service/     # Notification microservice
├── docker-compose.yml        # Infrastructure orchestration
├── docs/                     # Architecture diagrams, docs
├── README.md

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🔗 Communication

• API Gateway ⇄ Services: REST (HTTP)
• Between Services: Messaging (RabbitMQ/NATS)
  • OrderService emits order_created
  • InventoryService listens and adjusts stock
  • NotificationService listens and sends notification

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🚀 Features

👤 User Service

• Secure sign up & login
• JWT authentication
• Role-based access (admin/user)

🛍️ Product Service

• Create/list/delete products
• Fetch by product ID
• Simple MongoDB schema

🛒 Order Service

• Place new orders
• Validate users & product stock
• Emits order_created event

🏬 Inventory Service

• Listens to order_created
• Decreases stock or rejects if insufficient

📢 Notification Service

• Listens to events (order_created, etc)
• Sends notification (email/log)

🌍 API Gateway

• One entrypoint for frontend
• Reverse proxy, JWT verification
• Routes /products, /orders, /users to services

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🐳 Dockerized Infrastructure

Powered by docker-compose.yml:

• All microservices (with build contexts)
• MongoDB, PostgreSQL databases
• RabbitMQ or NATS for messaging
• Optional admin UIs: pgAdmin, Mongo Express, RabbitMQ dashboard

docker-compose up --build

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🛣️ Roadmap

• Add OpenAPI/Swagger docs for each service
• Service discovery and dynamic routing
• Production-ready monitoring & logging
• Integration with frontend (React/Angular)
• Advanced notification channels (SMS, Push)

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🤝 Contributing

Contributions, ideas, and feedback are welcome!
Feel free to open issues or submit pull requests.

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📜 License

MIT License. See LICENSE for details.

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👨‍💻 Author

Jawher Kallel
GitHub @JawherKl

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Made with ❤️ for scalable, real-world systems.

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