🛒 NodeJS Microservices: Order & Inventory System

Scalable and modular microservices architecture built with Node.js (NestJS & ExpressJS), PostgreSQL, MongoDB and Docker. It leverages RabbitMQ for event-driven communication, ideal for modern e-commerce and real-time systems.

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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 a single responsibility, clear separation, and scalable technologies.

• Tech Focus: TypeScript-first, RESTful APIs, event-driven messaging, containerised 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

NestJS]
        ps[Product Service

ExpressJS]
        os[Order Service

NestJS]
        isvc[Inventory Service

ExpressJS]
        ns[Notification Service

ExpressJS]
    end

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

    %% Messaging Layer
    subgraph "Messaging"
        rmq[[RabbitMQ

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

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	-	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)

• 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 entry point 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 for messaging
• Optional admin UIs: pgAdmin, Mongo Express, RabbitMQ dashboard

🧪 Docker Network & Setup

Before starting the app, create the Docker network:

docker network create \
  --driver=bridge \
  --subnet=172.21.0.0/24 \
  nodejs_network

Then run the entire system:

sudo docker-compose up --build -d

All services will be available on their respective internal IP addresses and ports, or via the API Gateway.

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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)
• [ ] Create CI/CD Pipeline with GitHub Actions

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🤝 Contributing

We welcome contributions, ideas, and feedback. 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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