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How to solve theDual Write problem using theOutbox Pattern with a pull and publish scheduler.

This project is a simple solution for theDual Write problem.

TheDual Write problem happens when:

• the application needs to write to two different systems in a single transaction
• the systems have different transactional boundaries
• if one of the writes fails, the other write can't be rolled back, leaving the system in an inconsistent state

Example:

Write to a database and to a message broker.

TheDual Write problem can be solved using theOutbox Pattern, which makes sure that if one of the writes fails, the system can still recover the state inside the transaction and roll back all the writes.

There are probably different ways to implement theOutbox Pattern, but this simple project implements it using:

• a database table calledoutbox that contains all the messages that need to be sent to the message broker
• a scheduled task that reads the messages from theoutbox table and sends them to the message broker

Then, once a service needs to write to theorders table, for example, it also writes to theoutbox table in the same transaction.

• Java 21
• Spring Boot 3.3.2
• Spring Data JDBC
• PostgreSQL
• Docker Compose
• Kafka