🛒 E-Commerce Microservices Platform

A production-style E-Commerce backend built using Spring Boot 3.5, Java 21, and a full Microservices Architecture. Services communicate asynchronously via Apache Kafka and are discovered through Eureka Service Registry, with all traffic routed through a centralized Spring Cloud API Gateway with Circuit Breaker fault tolerance.

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📋 Table of Contents

• Architecture Overview
• Microservices
• Tech Stack
• Event Flow
• API Reference
• Getting Started
• Environment Variables
• Design Patterns
• Author

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🏗 Architecture Overview

                        Client
                           │
                           ▼
              ┌────────────────────────┐
              │     API Gateway        │  ← Port 5000
              │  Spring Cloud Gateway  │
              │  + Resilience4j CB     │
              │  + Redis Rate Limiting │
              └────────┬───────────────┘
                       │  Load Balanced (Eureka lb://)
          ┌────────────┼────────────┐
          │            │            │
          ▼            ▼            ▼
  ┌──────────────┐ ┌──────────┐ ┌──────────────┐
  │Product Service│ │  Order   │ │   Payment    │
  │   Port 6002  │ │  Service │ │   Service    │
  │              │ │ Port 6001│ │  Port 6003   │
  └──────┬───────┘ └────┬─────┘ └──────┬───────┘
         │              │               │
         │         Kafka Events         │
         │    ┌─────────┴──────────┐    │
         │    │   Apache Kafka     │    │
         │    │  order-events      │◄───┘
         │    │  payment-events    │────►Order Service
         │    └────────────────────┘
         │
         ▼
    ┌─────────────────────────┐
    │   Eureka Discovery      │  ← Port 8761
    │   Server                │
    └─────────────────────────┘

  Each service → Own MySQL Database

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🧩 Microservices

Service	Port	Responsibility
API Gateway	5000	Single entry point, routing, circuit breaker, fallback
Discovery Server	8761	Eureka service registry — all services register here
Product Service	6002	Product & category CRUD, stock management
Order Service	6001	Place orders, manage order status, inter-service calls
Payment Service	6003	Process payments, listen to order events via Kafka

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🛠 Tech Stack

Layer	Technology
Language	Java 21
Framework	Spring Boot 3.5.0
API Gateway	Spring Cloud Gateway (WebFlux)
Service Discovery	Netflix Eureka
Messaging	Apache Kafka
Fault Tolerance	Resilience4j Circuit Breaker
Caching	Redis (API Gateway)
Database	MySQL (per service)
ORM	Spring Data JPA / Hibernate
Inter-service Calls	RestTemplate + Load Balancer
Build Tool	Maven

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⚡ Event-Driven Flow

User Places Order
       │
       ▼
  Order Service
  (saves order with PENDING status)
       │
       │ publishes → [order-events] topic
       ▼
  Payment Service
  (listens to order-events via @KafkaListener)
  (processes payment automatically)
       │
       │ publishes → [payment-events] topic
       ▼
  Order Service
  (listens to payment-events via @KafkaListener)
  (updates order status → CONFIRMED / FAILED)

Kafka Topics:

• order-events — Order Service → Payment Service
• payment-events — Payment Service → Order Service

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📡 API Reference

All requests go through the API Gateway at port 5000 with prefix /api/v1/

📦 Products — /api/v1/products

Method	Endpoint	Description
POST	/	Create a new product
GET	/	Get all products
GET	/{productId}	Get product by ID
PATCH	/{productId}/stock	Update stock quantity
DELETE	/{productId}	Delete product

🗂 Categories — /api/v1/categories

Method	Endpoint	Description
POST	/	Create a new category
GET	/	Get all categories
GET	/{id}	Get category with products

📋 Orders — /api/v1/orders

Method	Endpoint	Description
POST	/	Place a new order (triggers Kafka event)
GET	/{orderId}	Get order by ID
GET	/customer/{customerId}	Get all orders for a customer
PATCH	/{orderId}/status	Update order status

💳 Payments — /api/v1/payments

Method	Endpoint	Description
POST	/	Process a payment manually
GET	/order/{orderId}	Get payment details by order ID

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🚀 Getting Started

Prerequisites

• Java 21 — Download
• Maven 3.9+
• MySQL 8.0+
• Apache Kafka — Download
• Redis
• Docker (optional but recommended)

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Run Locally — Step by Step

Step 1 — Start Zookeeper & Kafka

# Start Zookeeper
bin/zookeeper-server-start.sh config/zookeeper.properties

# Start Kafka
bin/kafka-server-start.sh config/server.properties

Step 2 — Start Redis

redis-server

Step 3 — Start Discovery Server first

cd discovery-server
./mvnw spring-boot:run
# Visit http://localhost:8761 to see Eureka dashboard

Step 4 — Start all services (in any order)

# Terminal 1
cd product-service && ./mvnw spring-boot:run

# Terminal 2
cd order_service && ./mvnw spring-boot:run

# Terminal 3
cd payment_service && ./mvnw spring-boot:run

# Terminal 4 — Start Gateway last
cd apigateway && ./mvnw spring-boot:run

Step 5 — All traffic via API Gateway

http://localhost:5000/api/v1/products
http://localhost:5000/api/v1/orders
http://localhost:5000/api/v1/payments

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🔐 Environment Variables

Set these for each service before running:

# Order Service / Payment Service / Product Service
DB_URL=jdbc:mysql://localhost:3306/your_db_name?createDatabaseIfNotExist=true
DB_USERNAME=root
DB_PASSWORD=yourpassword

# Kafka
KAFKA_BOOTSTRAP_SERVERS=localhost:9092

# Redis (API Gateway)
SPRING_REDIS_URL=redis://localhost:6379

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🧩 Design Patterns

Pattern	Where Used	Purpose
API Gateway	apigateway	Single entry point for all clients
Service Discovery	Eureka + all services	Dynamic service registration & lookup
Event-Driven	Kafka + Order/Payment	Async, decoupled inter-service communication
Circuit Breaker	API Gateway (Resilience4j)	Prevents cascade failures, returns fallback
Load Balancing	lb:// in gateway routes	Client-side load balancing via Spring Cloud
Database per Service	All services	Each microservice owns its own data

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🗂 Project Structure

springBoot-Microservices/
├── apigateway/               # Spring Cloud Gateway + Circuit Breaker + Redis
│   └── config/
│       ├── RedisConfig.java
│       └── FallbackController.java
│
├── discovery-server/         # Netflix Eureka Service Registry
│
├── product-service/          # Product & Category management
│   ├── controller/
│   ├── service/impl/
│   ├── entity/
│   ├── mapper/
│   └── exception/
│
├── order_service/            # Order management + Kafka Producer
│   ├── controller/
│   ├── service/
│   ├── events/               # OrderCreatedEvent, PaymentCompletedEvent
│   ├── listener/             # PaymentEventListener (Kafka Consumer)
│   └── config/KafkaConfig.java
│
└── payment_service/          # Payment processing + Kafka Consumer/Producer
    ├── controller/
    ├── service/
    ├── events/
    └── listener/             # OrderEventListener (Kafka Consumer)

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👨‍💻 Author

Amar Deep Java Backend Developer

• 💼 LinkedIn: amar-maurya-backend
• 🐙 GitHub: @amar-deep-2025
• 🐦 Twitter/X: @TechWithAmar

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📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

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Built with ❤️ using Spring Boot 3.5 · Java 21 · Apache Kafka · Spring Cloud