Hey everyone,

One of the biggest headaches in distributed systems is ensuring data consistency when you need to update a database and notify another service (via Kafka/RabbitMQ) at the same time. If the DB commit succeeds but the message fails to send, your system is now inconsistent.

I put together a deep dive on the Transactional Outbox Pattern to solve this.

The scenario I used: A Pizza Shop ordering system. The Order Service saves the order, but if the message to the Inventory Service is lost, you have a hungry customer and a broken stock count.

What’s covered in the implementation:

The "Dual Write" Trap: Why u/Transactional isn't enough when external brokers are involved.

The Outbox Table: How to treat business logic and event publishing as one unbreakable unit.

The Poller Service: Setting up a scheduled relay service to query and publish unprocessed events.

Alternatives: Brief mention of CDC (Debezium) and the Saga Pattern for heavier requirements.

Tech Stack:

Java 21

Spring Boot 3.x

Kafka & Docker Desktop

PostgreSQL

I’ve included a full demo showing both a Success Scenario (eventual consistency) and a Failure/Rollback Scenario (simulating a 10/0 error to show how the Outbox prevents ghost messages).

Full Video Deep Dive: https://youtu.be/HK4tH17lljM

GitHub Repo: https://github.com/abchatterjee7

I'd love to hear how you guys are handling distributed transactions, are you team Outbox, or do you prefer CDC/Debezium for this?