In WavefrontTracingAutoConfiguration, it defines a WavefrontSpanHandler bean.
This passes an empty collection to the redMetricsCustomTagKeys in the constructor.
https://github.com/spring-projects/spring-boot/blob/0e67fbc855b714253e0b1fa7115d93f76c5618e3/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/wavefront/WavefrontTracingAutoConfiguration.java#L62-L69
Per this documentation in Wavefront, the redMetricsCustomTagKeys should be populated by the wavefront.tracing.red-metrics-custom-tag-keys property.
I believe this bean definition is the corresponding part for the property.
So, what the doc mentioned to work, I think populated values need to be passed to redMetricsCustomTagKeys rather than an empty set.
Comment From: wilkinsona
We can't proceed with this until we've got some input from the Wavefront team.
Comment From: oppegard
We (Wavefront team) recommend a new property be added to WavefrontProperties.java: management.wavefront.trace-derived-custom-tag-keys.
While the above property name is different from the Spring Boot 2 property (wavefront.tracing.red-metrics-custom-tag-keys), it matches the name used in other Wavefront Tracing usages documented at https://docs.wavefront.com/tracing_customize_spans_and_alerts.html.
This would be wired into the WavefrontSpanHandler that @ttddyy linked to.
Comment From: wilkinsona
Thanks, @oppegard.
Given that this was supported with Spring Boot 2 and the separate starter (albeit with a different property name), I think we should consider it to be a bug of omission in Spring Boot 3.0.
Comment From: oppegard
@wilkinsona that makes sense to me too. Thank you.