Building Reliable Event-Driven Systems: Event Schemas, Versioning, Contract Testing and Events vs Commands (part-1)

Short summary

This article argues that event-driven architecture is fundamentally about contracts, not just messaging. Published events become public APIs with invisible consumers, so removing a field can break downstream services just like breaking a REST endpoint. The piece covers event schema design, versioning, and the distinction between events and commands, positioning event design as an architectural rather than purely technical task.

• •Events are public APIs—invisible consumers make schema changes riskier than internal object changes
• •Event design is architectural work: deciding what information an event contains and how it evolves safely
• •Removing a field from a published event can break downstream services just as easily as breaking a REST response

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