event-contract-design

Designing an async event contract requires specifying producer and consumer ownership, event envelope structure, payload schema, topic naming, and evolution rules. The contract makes ordering, delivery, replay, idempotency, and dead-letter expectations explicit to prevent misaligned integrations.

Documenting event schema evolution involves defining explicit compatibility, versioning, and replay semantics. You must specify whether changes are additive or breaking, how correlation and causation cross boundaries, and what consumers expect during replay and dead-letter scenarios.

Defining idempotency and ordering rules requires explicit statements within the event contract. This ensures consumers understand the exact delivery, retry, and replay semantics, preventing duplicate processing and maintaining sequence integrity across queues or streams.

AsyncAPI and CloudEvents are suitable for documenting event APIs and structuring event envelopes. They provide the metadata framework to define payload schemas, required fields, optional fields, and deprecated fields for your asynchronous events.

Creating contract fixtures involves generating at least one positive and one negative fixture for deterministic validation. These fixtures are used for contract testing to verify that event envelope structures and payload schemas meet the specified requirements.

Dead-letter handling and replay semantics are needed to clarify consumer expectations during failure scenarios. Explicitly documenting these behaviors ensures that consumers can safely process or discard failed asynchronous events without degrading system reliability.