Schema Evolution and Compatibility

An order service adds a sales-channel field to its events so reporting can distinguish web orders from mobile orders. The producer change looks small, but several versions of the system now have to coexist: old consumers, new consumers, producers that teams are still deploying, and months of retained records.

A schema change succeeds only if the applications that encounter those records can still interpret them correctly. Registering a new definition does not update every consumer or rewrite old data.

In this chapter, we’ll examine compatibility from the reader’s perspective, work through concrete changes, and connect those rules to deployment, rollback, and replay.