How do I refer to traceparent from incoming request in startActiveSpan()?

[jdmarshall]

I'm trying to figure out how to associate traces in one service with spans in another. I would have expected this to be documented somewhere prominently but I have had no luck so far.

I'm using opentelemetry-sdk-trace-node along with the W3TracePropagator for outgoing requests but for incoming I haven't been able to discern actual logic in the instrumentation-express module.

[legendecas]

To create a span context from remote services, you can check out https://opentelemetry.io/docs/concepts/signals/traces/#context-propagation and https://github.com/open-telemetry/opentelemetry-js/blob/main/doc/propagation.md.

[jdmarshall]

Unfortunately that doesn't answer any questions. It documents that context can be propagated, but at no point does it discuss how that's achieved.

The answer to the question is in https://github.com/open-telemetry/opentelemetry-js/blob/main/api/src/propagation/TextMapPropagator.ts#L62 - api.propagation.extract() and api.propagation.inject(), which is mentioned more directly in
https://opentelemetry.io/docs/instrumentation/js/propagation/

[maxmcd]

Here's a github permalink to the manual propagation example that won't change if the code changes: https://github.com/open-telemetry/opentelemetry.io/blob/a30d87e97203973f5cdbd51cd407b5fd3aac3fb7/content/en/docs/languages/js/propagation.md?plain=1#L204

[jdmarshall]

@legendecas I haven't figured out the github to website mapping. How would I go about cleaning up these docs so the next person has an easier time? I'd like to add a crosslink at least, but it also seems like maybe the same concepts are being described in too many places and some fidelity is lacking. Might be that one of those pages should merge into the other...

[legendecas]

If you have any suggestions on https://opentelemetry.io/docs/instrumentation/js/propagation/, you can create a PR on https://github.com/open-telemetry/opentelemetry.io/blob/main/content/en/docs/instrumentation/js/propagation.md.