Article 14: Event-Driven Microservices with Kafka / RabbitMQ

1. Objective

Build event-driven microservices using a message broker.

2. Key Concepts

• Event-driven architecture
• Producer and consumer
• Topics / Queues
• At-least-once delivery

3. Kafka vs RabbitMQ (High Level)

Aspect	Kafka	RabbitMQ
Model	Log-based	Queue-based
Use Case	Event streaming	Message queuing
Ordering	Strong	Per queue

4. Event Flow

[Order Service] -> OrderCreated Event -> [Broker]
                                   -> Payment Service
                                   -> Inventory Service

5. Hands-On: Kafka Producer

kafkaTemplate.send("order-events", "OrderCreated");

6. Kafka Consumer

@KafkaListener(topics = "order-events")
public void consume(String message) {
    System.out.println(message);
}

7. Message Reliability

• Acknowledgements
• Retries
• Dead letter queues

8. Common Mistakes

• Ignoring idempotency
• Not handling duplicate events
• Tight coupling via event payloads

9. Interview Notes

• Event-driven systems scale well
• Kafka is widely used for streaming

10. Summary

Event-driven architecture enables loose coupling and scalability.

11. What’s Next

Add observability and resilience patterns.