Implement exactly-once CDC delivery using the transactional outbox pattern with Debezium and Kafka

Steps

1. Add an outbox table to the source database (e.g., outbox_events with columns: id UUID, aggregate_type VARCHAR, aggregate_id VARCHAR, event_type VARCHAR, payload JSONB, created_at TIMESTAMP).
2. In application code, write business entity changes and outbox rows in the same local database transaction; this guarantees atomicity — either both are committed or neither is.
3. Configure Debezium to capture only the outbox table and apply the OutboxEventRouter SMT: transforms.outbox.type=io.debezium.transforms.outbox.EventRouter, which routes events to Kafka topics based on aggregate_type.
4. The outbox table should be captured with a tombstone on delete (or truncated periodically) to prevent unbounded growth; use DELETE after confirmed Kafka acknowledgement or truncate via a scheduled job.
5. On the consumer side, implement idempotent processing keyed on the event id (UUID) to handle the at-least-once delivery guarantee of Kafka and prevent double-processing on retries.