Spring modulith event behavior wrt multiple instance of application

[thereisatechieinme]

In a Spring Modulith application with multiple instances, how are event publication, processing, and resubmission managed? Specifically, does only one instance listen to the published events, with the first instance to listen handling them? If an instance shuts down abruptly during event processing, will another active instance take over and handle the event reprocessing?

FYI: My application is deployed in AWS via Kubernetes and has 3 application replicas with 1 database instance.

[odrotbohm]

As the event distribution is per-application instance, an event in instance A would be processed by listeners within that instance. However, the event publication registry stores the information which listeners need to be invoked in a database. In case of an instance failure, the outstanding event publications can be resubmitted through the IncompleteEventPublications abstraction. In a multi-instance setup, you'd have to make sure that this functionality is only performed by a single instance. This in turn is usually implemented using a distributed lock. A popular library providing such functionality is SchedLock.

A lot of this (except the distributed lock approach) is covered in the reference documentation.