Event-Driven Microservices Architecture with RabbitMQ / Kafka / Redis

System Directive • Copy and Paste Below

Act as a Chief Systems Architect specializing in event-driven distributed microservices architectures and asynchronous messaging.

Design an event-driven architecture for the following business workflow to replace a synchronous, tightly coupled monolith.

### SYSTEM SPECIFICATIONS:
- Business Workflow: [WORKFLOW_NAME_E_G_ECOMMERCE_CHECKOUT_USER_ONBOARDING]
- Microservices Involved: [LIST_OF_MICROSERVICES]
- Message Broker Preference (RabbitMQ, Apache Kafka, AWS SQS/SNS, Redis Streams): [MESSAGE_BROKER]
- Eventual Consistency Tolerance & Transaction Guarantees: [CONSISTENCY_REQUIREMENTS]

### ARCHITECTURAL BLUEPRINT:
1. **Event Schema & Contract Definitions (CloudEvents Specification)**:
   - Structured JSON event payloads for key domain events (e.g. `OrderPlaced`, `PaymentProcessed`, `InventoryReserved`, `NotificationSent`).
   - Defining: `event_id`, `timestamp`, `aggregate_id`, `version`, and `payload`.
2. **Topic & Exchange Routing Topology**:
   - Publisher / Subscriber routing rules (Direct, Fanout, or Topic exchanges in RabbitMQ, or Partition keys in Kafka).
3. **Distributed Transaction Management (The Saga Pattern)**:
   - Choreography vs Orchestration Saga implementation for handling multi-service rollback (e.g. if payment succeeds but inventory reservation fails).
4. **Idempotent Consumer Implementation**:
   - Code pattern showing how worker services safely process duplicate messages without double-executing side effects.
5. **Dead Letter Queue (DLQ) & Poison Pill Protocol**:
   - Automated routing of corrupted messages to a DLQ with exponential retry backoff and monitoring alerts.

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