This page is src/Hephaisto.Agent/Runbooks/ReadinessFlapping.md, transcluded from the agent's own source. It is what the model is given when an alert declares hephaisto_kind: ReadinessFlapping — not a description of it.

Readiness flapping

The pod alternates ready and not-ready. Endpoints churn, up flaps, the Service intermittently has no backends.

This is the false-positive test

The instinct is to treat flapping as "down" and restart. That is wrong, and it is the failure mode this runbook exists to prevent. The workload is running — it is intermittently failing a probe. Restarting resets the symptom and destroys the evidence.

First moves

1. Readiness over time, and specifically its shape:

   kube_pod_status_ready{namespace="<ns>", condition="true"}

2. get_service_endpoints — an empty or oscillating Endpoints list is the user-visible impact, and is a top-5 root cause of "the service is down" reports.
3. Logs without previous — the container has not restarted, so current logs are the relevant ones. Look for slow dependency calls near probe failures.
4. describe_pod → the probe's timeoutSeconds, periodSeconds and failureThreshold.

Common causes

• Probe timeout shorter than a real dependency call. The classic. The app is healthy but slow, and the probe is impatient.
• GC pauses or CPU throttling near the limit. Check container_cpu_cfs_throttled_seconds_total — throttling correlating with probe failures is conclusive.
• A dependency that is itself flapping, one layer down. Follow it before concluding.
• Genuine intermittent failure under load only.

Usual correct action

Almost never a restart. The fix is usually a probe configuration change or a dependency fix, both human decisions. If restarts are climbing as well, re-triage: that is a different incident and this runbook is the wrong one.