This is part-2 of the article series on "Building Reliable Event-Driven Systems". In this article, we're going to explore Event Schemas.
5. Designing Event Schemas That Age Well
Once a team adopts event-driven architecture, the event schema quickly becomes one of the most critical design artifacts in the system. Unlike an internal Java class that is used within a single codebase, an event schema is consumed by multiple independent services. These services may be developed, deployed, and maintained by different teams, often evolving at different speeds. As a result, every field included in an event effectively becomes part of a contract that consumers may rely on.
Changing that contract later is rarely as simple as modifying a Java object. While internal models can evolve freely, event schemas must remain stable over time. Good schemas are designed to evolve gracefully, allowing systems to grow without breaking existing consumers. Poorly designed schemas, on the other hand, tend to accumulate compatibility issues that become increasingly difficult to manage.
At the core of this challenge is a simple but powerful question:
