[SOLVED] Using @SpanTag to add a custom attribute in traces

Using @SpanTag to add a custom attribute in traces

We are using micronaut tracing for distributed tracing. Which end up in new relic.

We want to add a new attribute/property which to a span, which appears in new relic within a trace. Suppose this property is in Object. I figured from the micronaut guide that adding a @SpanTag could be solution to it. But, I really do not have any other use of this property in the method, so it makes it an unused parameter. Is there another way?

Existing code:

@NewSpan("foo")
public void foo(Object obj) {
    otherService.bar(obj);
}

// to be
@NewSpan("foo")
public void foo(Object obj, @SpanTag("foo.property") String property) {
    // property argument is not used
    otherService.bar(obj);
}

Solution

You can inject a Tracer bean into your class.

import io.opentracing.Tracer;

public Foo {
   private final Tracer tracer;
   public Foo(Tracer tracer) { ... }

   @NewSpan("foo")
   public void foo(Object obj) {
      tracer.activeSpan().setTag("foo.property", property); // <1>
      ...
   }

Might not 100% correct, but should be close.