[OpenTelemetry] Model changes to allow OpenTelemtry context propagation

[stankiewicz]

Changes:

• dependencies definitions to otel
• WindowedValue interface change to expose context for propagation - context is not read by user
• changes are behind external_metadata experiment

Next PRs:

• propagation to windmill sink
• reading from windmill reader
• enabling default otel implementation for dataflow runner (v1 with propagation, v2 no propagation yet)

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[stankiewicz]

R: @sjvanrossum

[gemini-code-assist]

Summary of Changes

Hello @stankiewicz, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the foundational groundwork for integrating OpenTelemetry context propagation within Apache Beam. It involves updating OpenTelemetry dependencies, extending the internal data model (beam_fn_api.proto and WindowedValue interface) to carry trace context information, and implementing the necessary serialization/deserialization logic. These changes are part of an ongoing effort to enhance observability by enabling end-to-end distributed tracing across Beam pipelines, currently under an experimental flag.

Highlights

• OpenTelemetry Dependency Updates: Updated and added several OpenTelemetry dependencies in BeamModulePlugin.groovy and various build.gradle files to support OpenTelemetry context propagation.
• Protocol Buffer Extension for Trace Context: Modified beam_fn_api.proto to include traceparent and tracestate fields within the ElementMetadata message, enabling the serialization of W3C Trace Context.
• WindowedValue Interface Enhancement: Extended the WindowedValue interface and its implementations to include a getContext() method, allowing the OpenTelemetry Context to be associated with and propagated alongside data elements.
• OpenTelemetry Context Serialization: Introduced OpenTelemetryContextSerializer to handle the encoding and decoding of OpenTelemetry Context objects into and from the ElementMetadata of WindowedValue using the W3C Trace Context Propagator.
• Experimental Feature: These changes are implemented behind an external_metadata experiment flag, indicating an incremental rollout and testing approach.

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[stankiewicz]

/gemini review

[gemini-code-assist]

Code Review

The pull request effectively integrates OpenTelemetry context propagation into Apache Beam's core data structures and serialization mechanisms. This foundational change is well-implemented across various files, ensuring the Context is carried alongside WindowedValue elements. Key aspects include updating dependencies, extending the protocol buffer schema for traceparent and tracestate, modifying core WindowedValue interfaces and implementations to include the Context, and implementing robust serialization/deserialization logic via OpenTelemetryContextSerializer. The addition of a test case in WindowedValueTest.java validates the new functionality. The use of null for getContext() in specific overrides is consistent with the stated scope that the context is not yet consumed by users. Overall, this is a solid and necessary step towards comprehensive OpenTelemetry integration.

[kennknowles]

Will this change conflict with the GCP BOM? @suztomo do you think this is fine? We might just need to check them together manually.

[kennknowles]

OK... this way of doing things matches https://opentelemetry.io/docs/specs/otel/context/api-propagators/

But it does seem like a complicated way of doing the equivalent of

W3TraceContextPropagator.getInstance().setTracestate(elementMetadata.getTracestate());
W3TraceContextPropagator.getInstance().setTraceparent(elementMetadata.getTraceparent());

and

elementMetadataBuilder.setTracestate(W3TraceContextPropagator.getInstance().getTracestate());
elementMetadataBuilder.setTraceparent(W3TraceContextPropagator.getInstance().getTraceparent());

Other nit: did we not agree that the ElementMetadata object should be only implementation detail? This class and everything should be private since it is just for encoding/decoding utility. But potentially also you want to do the SETTER on an Builder and the GETTER on a WindowedValue. If it is implementation detail, hidden, then I don't care that much, but if it is public then we have to be careful about what classes we use.

[stankiewicz]

Yes, but I don't want to reimplement W3CTraceContextPropagator to have getTraceState /getTraceParent methods.

On nits - ValueInSingleWindow is not implementing WindowedValue interface now. Once it will, I can improve that.
Setter has builder already.