kaas-observability

The OTLP metrics + tracing bootstrap, the /healthz HTTP handler, and the byte-opacity tripwire counters.

The content of this crate — what gets exported where, the /healthz runtime view, why gauges read through lock-free snapshots — is covered in the Observability architecture chapter; this page is the code map.

Module map: bootstrap.rs (OTel SDK bring-up from OTEL_EXPORTER_OTLP_* env; metrics push OTLP/HTTP http/protobuf — the only dialect Prometheus's native OTLP receiver speaks; traces OTLP/gRPC), metrics.rs (the Arc-shared Metrics registry — global() returns a no-op registry before bootstrap, so pre-boot code and tests never nil-check), gauges.rs (the GaugeSource seam the broker feeds partition gauges through), health.rs (axum /healthz + /readyz; the RuntimeState trait), byteopacity.rs (the tripwire counters), k8s_api.rs (K8s API call metrics), topic_traffic.rs, tracing.rs (tracing-subscriber + OTel layer; every log line carries trace_id/span_id when a span is active).

Invariant callers must hold: gauge callbacks and RuntimeState implementations must never take hot-path locks — the gh #134 outage (a stuck NFS fsync starving the metrics pipeline) is why the storage engine exposes lock-free snapshots for exactly these readers.

Start reading at health.rs (the RuntimeState trait is a compact inventory of what the broker considers its own vital signs).