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, or in .docker.env when running it through Docker Compose. 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.