feat(trainer): add telemetry module for optional OpenTelemetry instrumentation

[prabindersinghh]

Summary

Adds kubeflow/common/telemetry.py as the shared OTel instrumentation
layer for the Kubeflow Python SDK, implementing the architecture proposed
in #164.

What this PR adds

kubeflow/common/telemetry.py

• get_tracer() — real OTel tracer or zero-overhead _NoOpTracer
  when opentelemetry-api not installed or KUBEFLOW_TRACING_DISABLED=1
• SpanNames — canonical span name constants for all SDK clients
• SpanAttributes — canonical attribute key constants
• configure() — one-call setup for Jaeger/OTLP/Console exporters
• _NoOpTracer / _NoOpSpan — safe fallback with empty method bodies

kubeflow/common/telemetry_test.py

• 15 tests covering NoOp path, env var disabling, context manager
  behavior, and naming convention validation
• Follows existing TestCase + pytest.mark.parametrize pattern

kubeflow/trainer/backends/kubernetes/backend.py

• KubernetesBackend.train() wrapped with root span
• wait_for_job_status() polling loop: per-iteration child spans
  with status_check span events
• All 47 existing backend tests pass with zero regressions

Span hierarchy produced

kubeflow.sdk.trainer.train [root]
├── kubeflow.sdk.trainer.get_runtime
├── kubeflow.sdk.trainer.create_trainjob
│ event: trainjob_submitted
└── kubeflow.sdk.trainer.poll_status [× N iterations]
attributes: poll.iteration, trainjob.status
events: status_check, job_reached_expected_status

Design decisions

Centralized in kubeflow/common/ — single module imported by all
SDK clients, enforcing consistent naming via SpanNames and
SpanAttributes constants.

Zero overhead — _is_otel_available() checks once and caches.
_NoOpTracer has empty method bodies. No allocation when disabled.

Optional dependency — opentelemetry-api not added to core
requirements. Users opt in via pip install 'kubeflow[telemetry]'.

Polling loop design — per-iteration child spans give full
visibility into state transitions for long-running jobs.

Validation

make verify → ruff check + format: PASSED
telemetry_test.py → 15/15 PASSED
backend_test.py → 47/47 PASSED (zero regressions)

Related

• Closes feat(common): add shared telemetry module for optional OpenTelemetry instrumentation #399
• Related to Integrate Kubeflow SDK with OpenTelemetry #164
• Companion to PR fix(trainer): fallback to cluster-scoped runtime on 404 in get_runtime #341

🚧 Draft — opening for early feedback as part of GSoC 2026 proposal work

[google-oss-prow]

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[Copilot]

Pull request overview

Adds a shared OpenTelemetry (OTel) instrumentation layer under kubeflow/common/ and wires initial tracing into the Trainer Kubernetes backend, aiming to provide optional, low-overhead observability for SDK operations.

Changes:

• Introduces kubeflow/common/telemetry.py with get_tracer(), configure(), canonical span/attribute constants, and NoOp fallbacks.
• Adds unit tests validating the NoOp behavior and naming/attribute conventions.
• Instruments KubernetesBackend.train() and wait_for_job_status() with root/child spans and span events.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
kubeflow/common/telemetry.py	Adds shared tracing helpers, exporter configuration, and canonical naming/attribute constants.
kubeflow/common/telemetry_test.py	Adds tests for NoOp fallback, env-var disabling, and naming/attribute conventions.
kubeflow/trainer/backends/kubernetes/backend.py	Wraps training + polling in spans and emits polling events/attributes.

[Rajneesh180]

Went through the full diff against the KubernetesBackend source. Solid foundation — the NoOp fallback design is the right call for an optional dependency. Some things I'd flag from working on the OTel Collector side:

Polling span creation (wait_for_job_status)
start_as_current_span(SpanNames.TRAINER_POLL_STATUS) is inside the for loop, creating a new child span per iteration. With timeout=600 and polling_interval=2, that's up to 300 spans per TrainJob. Wrapping the entire for loop in a single TRAINER_POLL_STATUS span and using span.add_event("status_check", {SpanAttributes.TRAINJOB_STATUS: trainjob.status}) per iteration would give identical Jaeger timeline visibility without the storage overhead. Also avoids POLL_TIMEOUT and POLL_INTERVAL attributes being duplicated 300 times — set them once on the parent span.

_NoOpSpan interface gap
Missing is_recording() -> bool and get_span_context(). If any downstream code or OTel instrumentation lib checks span.is_recording(), this raises AttributeError. Since this is a duck-type stand-in for opentelemetry.trace.Span, adding def is_recording(self) -> bool: return False would make it safer.

Exporter naming (_build_exporter)
exporter="jaeger" maps to OTLPSpanExporter — same path as "otlp". Since opentelemetry-exporter-jaeger was removed from the Python SDK, keeping "jaeger" as an option creates the impression of a different backend. I'd simplify to "otlp" and "console", noting in the docstring that Jaeger accepts OTLP natively on 4317.

_NoOpTracer allocation
get_tracer() returns _NoOpTracer() — new instance each call. In KubernetesBackend.__init__ it's fine since it's called once, but a module-level _NOOP_TRACER = _NoOpTracer() sentinel avoids unnecessary allocations if other code calls get_tracer() per-request.

Test coverage gap
The 15 tests validate the telemetry module in isolation (NoOp path, constants, env disabling). What's missing is an integration-level test that mocks KubernetesBackend, calls .train(), and verifies the span hierarchy/attributes with an InMemorySpanExporter. The existing 47 backend tests pass, but they don't assert on the instrumentation behavior.