How do I add a custom SpanProcessor to an auto instrumented service?

[fuleow]

I'm trying to add certain baggage entries to the server spans in my service that's auto instrumented by the agent. I have baggage propagation working and wrote my own SpanProcessor, but I am having a hard time adding my custom SpanProcessor. I stumbled across #2022 and the test repo is a really good reference of what I'd like to do (it has a DemoSpanProcessor). It's difficult to follow along the discussion in #2022 as there's been quite a bit of refactoring since then.

Can someone please point me in the right direction?

[trask]

hey @fuleow! check out https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/main/examples/distro

also, we are planning to support this without having to build your own custom distro, follow #2442 for future updates

[pskannusamy]

Hi @fuleow i am having the same issue on implementing the specifics of your case. But i could not really come to a point that works for baggage and span processor. My application is auto-instrumented by agent and I have added Baggage.current()
.toBuilder()
.put("mybag", "mybagvalue")
.build()
.makeCurrent(); in each request filter. But i am not seeing the baggage value on each child spans. Am i missing something or can you please let me know what are the all steps you have done to implement the baggage and span processor.?

[fuleow]

Hey makeCurrent() returns a Scope that's easiest to use in a try-with-resource block. The Javadocs has a good explanation and example. In a filter you would do something like

try(Scope ignored = ctxWithBaggage.makeCurrent()) {
  chain.doFilter(request, response)
}

[pskannusamy]

Hi Fuleow,

Thanks for your response, my question was can i use baggage for one specific attribute to be shown on every span/child span on a trace. And also it is not service to service call only within a single service, the parent span attributes values are not propagated to child span, hence i used baggage.
This is my sequence of actions i have wrote with auto instrumentation and i have enabled
-Dotel.propagators=tracecontext,baggage,b3,b3multi

but still i am not seeing the expected result of cloud.provider attributes to be seen in child spans

[pskannusamy]

Hey makeCurrent() returns a Scope that's easiest to use in a try-with-resource block. The Javadocs has a good explanation and example. In a filter you would do something like

try(Scope ignored = ctxWithBaggage.makeCurrent()) {
  chain.doFilter(request, response)
}

Hi @fuleow how did you confirm that baggage propagator worked for you. i have a similar usecase like yours but i am having an hardtime getting it to validate whether baggage propagation is working. When i set afield/key in baggage on first request and within the service if i try to see if that baggage is available with the key or not using the log but baggage is coming as empty? am i missing something?

[fuleow]

Your SpanProcessor needs to return true for isStartRequired. I used the demo included in this repo to write tests for validation.