Cross-process tracing

[main--]

I'm wondering if it's possible to sort of "continue" a trace from within another process. So if I have a client that begins a trace and then this client makes a call to a sever, both can report their tracing data (through opentelemetry in my case) and I end up with a trace that includes both the server-side and the client-side action.

I tried sending the Span's Id and specifying it as the parent span on the other side, but tracing-subscriber's Registry clearly doesn't like that:

tracing/tracing-subscriber/src/registry/sharded.rs

Line 273 in 2b3aa06

.unwrap_or_else(|| panic!("tried to clone {:?}, but no span exists with that ID", id));

And in opentelemetry I would also have to make them share a trace_id somehow. However, after a quick peek at tracing-opentelemetry's code it seems to me like trying to build a top-level span with opentelemetry directly also won't work, since it appears to rely exclusively on the Registry to find parent spans.

[davidbarsky]

I'm wondering if it's possible to sort of "continue" a trace from within another process. So if I have a client that begins a trace and then this client makes a call to a sever, both can report their tracing data (through opentelemetry in my case) and I end up with a trace that includes both the server-side and the client-side action.

Sorry for the delay in responding. This is possible, yes.

I tried sending the Span's Id and specifying it as the parent span on the other side, but tracing-subscriber's Registry clearly doesn't like that:

Span IDs are opaque identifiers that can only be used in a single process—the Registry's documentation calls this out, but perhaps this should be in a more prominent location.

And in opentelemetry I would also have to make them share a trace_id somehow. However, after a quick peek at tracing-opentelemetry's code it seems to me like trying to build a top-level span with opentelemetry directly also won't work, since it appears to rely exclusively on the Registry to find parent spans.

You will be able to use tracing-opentelemetry to propagate trace_id information, primarily through OpenTelemetrySpanExt trait. While this example does not include Jaeger, it might set you on the right direction.

Does that help a bit?

[main--]

Thanks, I think OpenTelemetrySpanExt is exactly what I was missing!