Add attributes while using autoconfigured javaagent

[mindscratch]

I like the idea of using the autoconfigured JavaAgent to support tracing in my gRPC service, but I was wondering if it's possible to add attributes or baggage to the spans somehow? Perhaps a mix of autoconfigured + manual? Or would I have to just go all manual?

[trask]

hi @mindscratch! check out https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/docs/manual-instrumentation.md#manual-instrumentation

[mindscratch]

@trask Thanks, that seems to work for the one method that processes the incoming request, but then I invoke a auto-generated gRPC client to call another service..and that span doesn't have the attribute. Is it possible to force the attribute to propagate through? Maybe a custom interceptor?

[trask]

oh yes, adding custom attributes to CLIENT spans is tricky in general. it's definitely worth trying a custom interceptor. though i'm not certain we are managing the interceptor order correctly, so it may work now and not later if we make a change: #2923

the general mechanism for adding custom attributes to CLIENT spans involves putting the attribute into the Context and then using a SpanProcessor to populate the attributes from the Context.

if you want to copy the attribute from the parent span down to the CLIENT span, you can skip putting the attribute into the Context and just write a SpanProcessor to copy it down, e.g. https://github.com/microsoft/ApplicationInsights-Java/blob/main/agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/init/InheritedAttributesSpanProcessor.java

once you get into SpanProcessors, you will have to write an agent extension: https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/main/examples/extension#introduction

in the future, hopefully a more standard mechanism for this will evolve, maybe using Baggage and stamping baggage onto spans