Kafka: Schema evolution needs a compatibility rule

BACKWARD compatibility lets new consumers read old data - the usual default with a schema registry.

Code

// v1
{"orderId": 42, "total": 149.5}

// v2 - BACKWARD compatible: new field has a default
{"orderId": 42, "total": 149.5, "currency": "INR"}

// NOT compatible - removing a required field, or renaming one
{"id": 42, "total": 149.5}

Output

BACKWARD: new consumer, old data  (add optional fields, remove optional ones)
FORWARD:  old consumer, new data
FULL:     both

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Published 2026-08-11