Event ticketing system built with Spring Boot microservices architecture, featuring event-driven communication via Kafka and secure API gateway with OAuth2 authentication.

┌─────────────┐
│ API Gateway │ :8090 - Entry point with OAuth2 + Circuit Breaker
└──────┬──────┘
       │
       ├──────► Inventory Service :8080 - Event & venue inventory management
       │
       └──────► Booking Service   :8081 - Ticket booking + Kafka producer
                      │
                      │ Kafka (BOOKING_TOPIC)
                      ▼
               Order Service      :8082 - Order processing + Kafka consumer

• Java 21
• Spring Boot 3.5.7
• MySQL 8.0
• Apache Kafka
• Keycloak (OAuth2)
• Flyway (DB Migration)
• Resilience4j (Circuit Breaker)

• JDK 21
• Maven 3.6+
• MySQL 8.0
• Apache Kafka 3.0+
• Keycloak 21+ (optional, for API Gateway)

CREATE DATABASE ticketing;

Each service needs a .env file. Copy from examples:

cp inventory-service/.env.example inventory-service/.env
cp booking-service/.env.example booking-service/.env
cp order-service/.env.example order-service/.env
cp api-gateway/.env.example api-gateway/.env

Update database credentials in each .env:

DB_USERNAME=root
DB_PASSWORD=your_password

Start each service in separate terminals:

# Terminal 1
cd inventory-service && mvn spring-boot:run

# Terminal 2
cd booking-service && mvn spring-boot:run

# Terminal 3
cd order-service && mvn spring-boot:run

# Terminal 4
cd api-gateway && mvn spring-boot:run

1. Get available events (via API Gateway)

   GET http://localhost:8090/api/v1/inventory/events

2. Book tickets (via API Gateway)

   POST http://localhost:8090/api/v1/booking/book
   {
     "userId": 1,
     "eventId": 1,
     "ticketCount": 2
   }

3. Booking service publishes event to Kafka topic BOOKING_TOPIC

4. Order service consumes event and creates order in database

5. Order service updates inventory via REST call to Inventory Service

ticket-book-microservices/
├── inventory-service/    # Event & venue management
├── booking-service/      # Ticket booking + Kafka producer
├── order-service/        # Order processing + Kafka consumer
├── api-gateway/          # API Gateway with OAuth2

Inventory Service

• Event and venue CRUD operations
• Real-time capacity tracking
• REST API for inventory queries

Booking Service

• Ticket booking validation
• Kafka event producer
• Inventory availability check

Order Service

• Kafka event consumer
• Order persistence
• Inventory update via REST client

API Gateway

• OAuth2 authentication (Keycloak)
• Circuit breaker pattern
• Request routing to downstream services
• Aggregated API documentation

# From root directory
for dir in inventory-service booking-service order-service api-gateway; do
  cd $dir && mvn clean install && cd ..
done

cd <service-name>
mvn test

Flyway migrations run automatically on application startup. Migration files located in src/main/resources/db/migration/.

• API Gateway enforces OAuth2 authentication via Keycloak
• Database credentials stored in .env files (not committed to git)
• Public endpoints configurable via SECURITY_EXCLUDED_URLS

API Gateway exposes Circuit Breaker health metrics:

GET http://localhost:8090/actuator/health