Testing Metrics

Unit tests can inspect emitted metrics using the test metric provider from docs_rs_opentelemetry; tests using the shared context can call TestEnvironment::collected_metrics. For an end-to-end check, the Docker Compose setup provides an OpenTelemetry Collector configured to log the metrics it receives.

Start the collector with:

$ just compose-up-metrics

Configure the docs.rs process to export OTLP metrics to it:

OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317

Put this setting in .env when running docs.rs on the host. For processes running through Docker Compose, use http://opentelemetry:4317 instead. Restart the application after changing its environment.

The collector uses OTLP over gRPC on port 4317 and writes received metrics to its logs. Follow them with:

$ docker compose logs --follow opentelemetry

If OTEL_EXPORTER_OTLP_ENDPOINT is unset, docs.rs uses a no-op metric provider.