The core engine is responsible for executing business logic. When this is stateful, the state of the engine is persisted at the end of the service invocation. On top of that, the engine also typically sends out events around what is happening during execution (the engine already aggregates these so they can be sent out in bulk at the end of the service invocation too). Potentially, there could be inconsistency when performing these two types of actions.

A solution is to implement the outbox pattern to handle the actions in one transaction: 

• https://debezium.io/blog/2019/02/19/reliable-microservices-data-exchange-with-the-outbox-pattern/
• https://dzone.com/articles/implementing-the-outbox-pattern

For this story, a PoC, which uses MongoDB as persistence solution and Debezium as message relay, is created to implement the outbox pattern to manage the consistency of kogito runtime persistence and events.