[http-plugin] Include trace ID in response headers for incoming requests

[OlivierAlbertini]

Hello

I would like to add the trace id in the response headers for incoming requests.
We would like to move the discussion in this repo (ref: open-telemetry/opentelemetry-js#166).

Is your feature request related to a problem? Please describe.

• Having trace id in headers can help to debug slow requests we see in
  the browser by looking up the trace ID found in response headers.
• It can help the propagation

Describe the solution you'd like

• Inject trace id in the response header and only for incoming requests.
• Make this feature optional and disabled by default

Thanks. Let me know if I can help.

[mtwo]

FYI @bogdandrutu @AloisReitbauer @discostu105 @SergeyKanzhelev @iredelmeier

We've discussed this before at meetings of the W3C TraceContext group (which is mostly composed of OpenTelemetry contributors) and I think that it's a good idea, though we need to think through the implementation. Returning a trace context header in responses benefits the following scenarios:

• It enables a basic case of delegated sampling, where the outermost layer of an application (typically a load balancer) can defer sampling decisions to the layer beneath it while still generating spans
• This can assist with debugging across organizational / trust boundaries, where the caller of an API can record the trace ID returned to them by the API provider

I believe that there are a few unresolved conversations around whether TraceState should be returned as well.

[SergeyKanzhelev]

I triaged this as "future for now", meaning likely not in 1.0. Please reply back if this needs to be addressed earlier

[jmacd]

The W3C committee is moving forward with a proposal, see w3c/trace-context#365
Closing for now.