Event-Driven Messaging

Design for at-least-once delivery unless the complete system proves stronger semantics.

Event contract

• Use an immutable event envelope with eventId, eventType, occurredAt, schemaVersion, and payload.
• Treat published schemas as APIs. Add fields compatibly and never silently change meaning.
• Put correlation and causation IDs in headers or the envelope.
• Do not publish JPA entities or framework-specific serialization shapes.

Producer rules

• Publish only after the originating state change is durable.
• Use a transactional outbox when database state and broker publication must agree.
• Use deterministic partition keys when per-aggregate ordering matters.
• Configure delivery timeout and acknowledgements explicitly.

Consumer rules