fix(metrics): serve lightweight /healthz on metrics port - #12
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promhttp was mounted as the root handler, so kubelet probes to /healthz on :4001 received the full Prometheus exposition (10-26MB on hot pods). Concurrent Gather with scrapes exceeded probe timeouts and restarted pods. Route /healthz|/health to a cheap 200 OK; keep /metrics (and /) as the exposition. Co-authored-by: Cursor <cursoragent@cursor.com>
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Summary
/healthzand/healthreturn a cheap200 OKwithout calling PrometheusGather./metrics(and/for back-compat) aspromhttp.Handler().Why
Prod DaemonSet probes hit
:4001/healthz. That port usedpromhttp.Handler()as the root handler, so every path returned the full exposition. On hot pods (PreferSameNodeskew) that payload is 14–26MB / 80–137k series. Concurrent Gather with Prometheus scrapes pushed scrape duration to 5–10s, exceeding kubelettimeoutSeconds: 5and causing liveness kills (internal-erpc-zczc4, probe failures onfrd5n).Real
:4000/healthcheckstays healthy at ~4–13ms during the same windows — the process was fine; the probe target was wrong/expensive.Test plan
go test ./erpc/ -run TestNewMetricsHandler:4001/healthzreturnsOKin <10ms and is not a Prometheus dump:4001/metricsstill scrapes normally:4000(defense in depth either way)Made with Cursor