OpenTelemetry tracing support?

[stefee]

Does undici work out of the box with node auto-instrumentation for OTEL? https://github.com/open-telemetry/opentelemetry-js-contrib/tree/main/metapackages/auto-instrumentations-node

The auto instrumentation includes shims for the node core modules node:http, node:net, etc.

It seems that trace propagation across service boundaries will only work for libraries that are using http.request under the hood (e.g. node-fetch). Does undici use http.request under the hood or does it use something more primitive like tcp.connect instead? This might prevent the OTEL instrumentation from injecting the headers required for traces to get propagated?

I also discovered that this package exists, but it might make sense to provide an "official" integration or recommendation: https://github.com/gadget-inc/opentelemetry-instrumentations

Update: Twitter user confirmed to me that it doesn’t work out of the box with the auto instrumentation
https://twitter.com/isntitvacant/status/1524869221280190464?s=21&t=PquRXpxyYTBYaDlk2uA9cA

[mcollina]

Correct. Would you like to help and implement this? It would need to use https://github.com/nodejs/undici/blob/main/docs/api/DiagnosticsChannel.md to implement everything and restrain from massive monkeypatching. We will be happy to respond to any questions.

[stefee]

Hang on a sec - I take that back. I should learn to read. https://github.com/nodejs/undici/blob/main/docs/api/DiagnosticsChannel.md#undicirequestcreate

request.addHeader('hello', 'world')

Should give us what we need.

[stefee]

I think we were crossing wires @mcollina - OTEL context propagation is not handled automatically by undici, it needs to be handled by the instrumentation by injecting headers. But this can be achieved using diag channels rather than needing to monkey-patch, you’re right.

[mcollina]

monkey-patching is (mostly) needed because libraries can't maintain the asynchronous context across callbacks and promise chains. The problem is not to add headers in the right moment, but rather make sure the information to put there is available. This is a problem for a lot of libraries. We commit to fully support async_hooks and ALS in undici.

[stefee]

I’m looking at OTEL in more detail now and will update here open-telemetry/opentelemetry-js-contrib#1021

[Flarna]

I think from OTel point of view the use of TracingChannel would be a better fit instead of simple channels. It avoid the need of an enterWith like API.

An enterWith() like API is not part of the TC39 proposal for AsyncContext and therefore likely not future proof.