Event Driven Architecture

# Event Driven Architecture (EDA)

## 1. Core Principles
EDA is a software architecture pattern where the flow of the system is determined by events—significant changes in state. Unlike request-response models, producers emit events without knowledge of consumers.

## 2. Key Components
- **Event Producers:** Services that detect state changes.
- **Event Channels/Brokers:** Infrastructure (Kafka, RabbitMQ, Pulsar) for event routing.
- **Event Consumers:** Downstream services reacting to events.
- **Event Store:** Immutable log of past events for state reconstruction.

## 3. Communication Patterns
- **PubSub:** Decoupled messaging where subscribers filter topics.
- **Event Streaming:** Continuous flow of data processed in real-time.
- **Event Sourcing:** Storing state as a sequence of events rather than current state snapshots.

## 4. Architectural Patterns & Trade-offs
- **CQRS:** Separating read and write models, often synchronized via events.
- **Saga Pattern:** Managing distributed transactions across microservices using compensating events for rollbacks.
- **Challenges:** Eventual consistency, distributed tracing complexity, idempotency requirements, and schema evolution (Avro/Protobuf).

## 5. Implementation Strategy
1. Define bounded contexts and domain events.
2. Select transport layer (e.g., Kafka for high throughput, RabbitMQ for complex routing).
3. Implement idempotent consumers to handle duplicate deliveries.
4. Establish a Schema Registry to manage event versioning.