Is it possible to end a span created from context propagation?

[MrRickwi]

We are instrumenting a workflow engine with trace support. We have a plugin that listens for the START and END events of a workflow. In the START event, we open a span and inject this into the workflow. In the END event, we would like to extract the injected span (traceparent, ...) from the workflow and end this one.

However, the following code seems not work maybe due to the fact that the span we get there is an ImmutableSpan.

START:

      Span span = tracer.spanBuilder(execution.getProcessDefinitionId() + ":" + execution.getProcessInstanceId()).startSpan();
      // Insert the new span into the current workflow
      try (Scope scope = span.makeCurrent()) {
        openTelemetry.getPropagators().getTextMapPropagator().inject(Context.current(), execution, TextMapInjectAdapter.SETTER);
      }

END:

    Context extractedContext = openTelemetry.getPropagators().getTextMapPropagator().extract(Context.current(), execution, TextMapExtractAdapter.GETTER);
    try (Scope extractedScope = extractedContext.makeCurrent()) {
      Span span = Span.fromContext(extractedContext);
      span.end();
    }

Any ideas around there? Remembering the span in code is not feasible because the workflow engine may be restarted while the workflow is running, thus loosing any transinet information in the workflow.

[jkwatson]

Hi @MrRickwi . You are correct in finding that this is not possible. In OpenTelemetry, propagated spans are assumed to have their lifecycle fully managed by the creating process. In your case, you probably need to model this as two separate spans, connected either via standard parenting, or via a span Link, depending on how you would like to see the structure.

[jkwatson]

Is there a reason you can't just have the start and end be two different spans, with start being the parent of end?

[MrRickwi]

@jkwatson, in my first experiments I created a span in START, injected it into my workflow context, and ended it there. As a result, I saw only the start span and no child spans, I assume due to the fact that the injected start span already was ended when new spans where added as child. Then I tried never to close the start span, and as a result I see nothing - makes sense, the span is still active and not shown in Jaeger. So that is the reason why I try to end the start span exactly where it should end - at the end of the workflow. If there is another approach, I would appreciate it.

[jkwatson]

As I said..I think your only approach here is to have two spans. One for the start of the process and one for the end of the process. Inject the start-of-process span into an execution context of some sort, then extract it and use it as the parent of the span that tracks when your process gets ended. OpenTelemetry doesn't support your use-case as you want to do it. If the end of the process might take place on a different machine/JVM, then you have to have it be a 2nd span.

[MrRickwi]

So I will give it a try. Last question: In your approach, would you end the first span after injecting it into the execution context?

[jkwatson]

I think so, yes. Effectively the span is "start the job", and once it's been kicked off and submitted, then the span would end.