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ADR: Compile-time URI retention for step latency metrics

  • Status: Accepted (implemented in OpenSpec change steplatency; bd rc-cd7o)
  • Amends: ADR-0042, ADR-0066

Context

Route compilation currently turns a To(uri) builder step into a processor without retaining the authored URI. The OTEL tracing adapter can therefore record route and exchange metrics, but cannot attribute call-time latency to a specific outbound step. The dynamic-label metrics API already supports the required histogram labels.

Decision

CompiledStep::Process carries optional compile-time URI metadata. The compiler stamps the raw declared URI only for To steps before endpoint resolution and interception. Tracing carries this metadata into TracingProcessor and records step_duration_secs with route and to_uri labels when the duration lever is enabled and the attempt is a call-time attempt. A failed call-time attempt also records the histogram; the observation measures the failed attempt. Readiness attempts never record the family.

The label contains trusted, operator-authored route configuration. It is not derived from exchange data and is not the resolved runtime target. The existing open-label lint justification is required because URI cardinality is an intentional part of this profiling surface.

Consequences

Operators using camel run --otel receive per-to_uri duration series without changing component contracts or benchmark tooling. Every compiled process step stores one optional shared string, and route composition must preserve it. Readiness attempts remain excluded from duration histograms, consistent with ADR-0066. Dynamic or exchange-derived URI attribution is not provided.

Implementation evidence

Task 2.1 shipped the emission in camel-core. Unit tests in tracer_tests.rs pin the label set, the failed-call emission, the include_duration gate, the duration-lever gate, and the readiness exclusion. Task 3.1 pins the exported family at the integration tier in crates/camel-test/tests/metrics_wiring_test.rs: otel_metrics_expose_step_duration_family drives one exchange through a To("direct:orders") route on the OTEL-enabled wiring probe and asserts the collector observed step_duration_secs labeled with route and to_uri. otel_metrics_omit_step_duration_for_processor_route drives a processor-only route through the same wired path and asserts the family has zero data points.