java-outbox-idempotency

Achieve exactly-once messaging in Java microservices by applying the transactional outbox pattern with atomic writes and idempotent consumer dedup strategies to prevent double-publish and inconsistent state across services.

The transactional outbox pattern writes events to an outbox table within the same database transaction as business data. You need it when reliable integration event delivery is required across microservices without dual-write inconsistencies.

Choose polling-based relay for simpler outbox event routing to messaging systems, or CDC-based routing for lower latency and reduced database load when capturing transaction log changes in Java microservices.

Make message consumers idempotent by implementing dedup strategies and idempotency guards that track processed messages, ensuring duplicate event deliveries from the messaging system do not trigger multiple state changes.

Duplicate messages and inconsistent state occur when writing to the database and messaging system separately. Using a transactional outbox captures both writes atomically, ensuring reliable event delivery after commit.

The outbox pattern integrates with existing Java microservices by writing the outbox schema within your current database transaction boundaries, requiring no new dependencies to ensure reliable integration events.