Building Reliable Event-Driven Systems: Event Schemas, Versioning, Contract Testing and Events vs Commands (5/5)

Short summary

Part 5 of a series on event-driven systems covers production realities: events are delivered not guaranteed, so consumers must be idempotent using event IDs. Ordering cannot be assumed due to network latency and parallel processing, so consumers should validate state before processing. Correlation IDs make distributed workflows traceable, and immutable events form a natural audit trail.

• •Duplicate delivery is expected — enforce idempotency at the business logic level with event IDs
• •Don't rely on strict event ordering; design consumers to tolerate reordering
• •Use correlation IDs to trace multi-service workflows
• •Events are immutable and form a natural audit trail

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