Propagating custom headers inter-process

[vim-daniel]

I'm pretty new to open telemetry,
And I'm trying to create a POC that will allow me to send a request from a browser to a service with some header and then have that service propagate that header along to another service.

Browser -> Header Pass-along -> Service A -> request to Service B + Header Pass-along -> Service B

Both of the services are nodejs based, I've been able to see the traceId attributes propagating between the services.

I tried to read the docs and saw a lot of docs about the concept of maybe using Baggage or propagation.inject & propagation.extract.

But I haven't been able to make it work, I've tried playing with the @opentelemetry/instrumentation-http options but
it only added attributes in the same service and they weren't propagated to the other service..

I saw some existing discussions about similar topics but could figure out where to start from 🥲

Hope someone from the community might be of help! thanks 🫶🏻

Minimal reproduction:
https://stackblitz.com/edit/express-simple-b26ph6?file=README.md

[legendecas]

Would you mind sharing a code snippet or a minimum code repository that doesn't work so that we can help to investigate what the right course is for you?

[vim-daniel]

Sure,
I've created a minimal setup in here:

https://stackblitz.com/edit/express-simple-b26ph6?file=README.md

[psk001]

@vim-daniel did you get any solution for it? I'm struck at the same issue.

[legendecas]

The option headersToSpanAttributes is extracting span attributes from the http headers. However, span attributes are not propagated to the downstream services.

For the need to set custom headers to be sent to the downstream services, I've created a draft doc about how to implement your own propagator to do it: #3351

[vim-daniel]

Amazing! I've update the minimal setup and it's now working :)
Thank you 😄