Event externalization bootstrap should log which event types it's configured to externalize.

[odrotbohm]

The analysis of this sample project here made obvious, that it's difficult to detect that events from modules not included in test runs are not subject to application module scoped integration tests. A simple log message that describes which events are selected for externalization.

We should add a bit of debug-level logging to help to diagnose such problems.

[sangjun121]

Hi! You previously asked if I was interested in this issue, and after reading through the code, I’ve decided to give it a try

I was thinking of updating the supports(…) method in DefaultEventExternalizationConfiguration to add the logging. Does that sound like the right place?

Also, one quick question: would it be acceptable to add a logging dependency to spring-modulith-events-api for this purpose?

Thanks in advance!

[odrotbohm]

I wouldn't want to issue that log over and over again on each attempt. Especially as the predicate makes it difficult to produce human-readable output why we select a particular event for externalization or not.

I think EventExternalizationAutoConfiguration.eventExternalizationConfiguration(…) would be a good place to log the configured setup, as it's the place in which we create the configuration to be applied for the rest of the application's runtime. Slf4j should be on the classpath for that module already.

Oh, I don't think we need any elaborate testing, as it's log output only.

[sangjun121]

I have a quick clarification regarding the debug logging for event externalization.

In the EventExternalizationAutoConfiguration.eventExternalizationConfiguration() method, it looks like we only configure the filter using EventExternalizationConfiguration.defaults(...), and the actual decision about whether an event is externalized or not happens later when the predicate is applied.

Given that, I wanted to confirm your intention:
Are you suggesting we simply log the configuration setup itself (such as base packages and applied filters), or did you mean to also log which events are actually going to be externalized?

The reason I ask is that determining the actual externalized events at this point would likely require scanning the entire classpath — which might be beyond the intended responsibility of this configuration class and could introduce unnecessary overhead.

Thanks in advance for your guidance!

[odrotbohm]

Are you suggesting we simply log the configuration setup itself (such as base packages and applied filters), or did you mean to also log which events are actually going to be externalized?

The former.

[sangjun121]

Thank you for the clarification!
I’ve made the necessary changes based on your feedback and opened a PR with the update.
Appreciate your time and guidance!

[odrotbohm]

That's polished and merged, thanks!