Issue in converting between OTEL and APM context

[rubvs]

Describe the bug

Information seems to be getting lost between converting from an APM context to OTEL context.

1. If we have a OTEL parent span and APM child span, we can see full relationship in Kibana. The figure below shows how we go from elasticHandler (otel) -> Streaming (apm) -> Semaphore.Acquire (apm)

2. The issue arises when we want to go from an APM span back to an OTEL span. In this case, we do not observe the last span (Semaphore.Acquire) in Kibana.

To Reproduce

1. Create an OTEL parent span. Then an APM child span, followed by another APM child span. View in Kibana
2. Create an OTEL parent span. Then an APM child span, followed by an OTEL child span. View in Kibana

Expected behavior

Spans and Span Links that go from OTEL context to APM context doesn't work.

[dmathieu]

Nice find.
It looks like this is because the APM span is a child span. We only look for transactions when checking parent spans from apm.

apm-agent-go/module/apmotel/tracer.go

Lines 77 to 79 in 2b38f4b

	if tx := apm.TransactionFromContext(ctx); tx != nil {
	parent = &span{tx: tx}
	}