[Misc] Add OpenTelemetry support

[ronensc]

This PR adds basic support for OpenTelemetry distributed tracing.
It includes changes to enable tracing functionality and improve monitoring capabilities.

I've also added a markdown with print-screens to guide users how to use this feature. You can find it here

FIX #3789

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[PRATIBHA-Moogi]

@rkooo567 can you please review this PR raised by Ronen. Thanks.

[rkooo567]

yep will do tmrw!

[ronensc]

Rebased to fix merge conflicts.

[gyliu513]

Thanks for the adoption of otel llm semantic convetion, this is great!

[saurabhjha1]

Great. also do we have a holistic view of different observability metrics in vLLM?

I see another effort here: #5041

[ronensc]

We have this issue: #3616 (comment)

[ronensc]

Added a commit to pass all unit tests.
Currently, a trace is created only for non-embedding requests because, for embedding requests, first_token_time isn't set, which is required for reporting TTFT. Additionally, sampling_params doesn't exist for embedding requests, so there is no point in reporting its metadata.

[nirga]

Can I suggest using the constants from https://github.com/traceloop/openllmetry/blob/main/packages/opentelemetry-semantic-conventions-ai/opentelemetry/semconv/ai/__init__.py
?
We keep them up to date with the decisions we're making in the otel semantic conventions working group

[ronensc]

Thanks for your suggestion! I've added a dependency on opentelemetry-semantic-conventions-ai and extended SpanAttributes with the missing constants.

[rkooo567]

Code itself looks good to me. My main concern is that we should probably not include this by default? This requires to setup Jaeger (or other tracing tools), and this seems pretty heavy requirements for every user.

That said, it'd require 3 changes.

• remove the requirements from requirements-common.txt
• init_trace should try importing it and becomes no-op when packages are not downloaded.
• Fail the request if tracing is not enabled.

cc @simon-mo for thoughts!

[rkooo567]

QQ: what's the e2e overhead of this API? Can you measure and lmk for prompt length 512 output length 128?

[simon-mo]

It needs to be opt-in (i think it is already?), similar to TGI:

text-generation-inference is instrumented with distributed tracing using OpenTelemetry. You can use this feature by setting the address to an OTLP collector with the --otlp-endpoint argument.