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  1. IL-0059 Single-master Kubernetes control plane kept dying because the kubelet restarted a healthy etcd on a failing kubeadm liveness probe
    NRE Labs2018
    Symptoms

    The daily NRE Labs statistics showed lesson activity collapsing, and kubectl could not reach the cluster: `The connection to the server 1.2.3.4:6443 was refused - did you specify the right host or port?`

    Control plane unresponsiveProbe failuresService outage
    Trigger

    Unknown. The liveness probe that kubeadm writes into the etcd static pod manifest (an `etcdctl get foo` against 127.0.0.1:2379, failureThreshold 8, timeoutSeconds 15) started failing. The author first suspected GCP maintenance the night before, but could not reproduce the probe failure by hand and does not know why it began.

    Root cause
    unknown
    Component
    etcdkubeletKubernetes API server
    Contributing factor
    Single point of failureUnreviewed defaultsHarmful manual actionIgnored early signalMonitoring blind spot
    Detection

    The author saw lesson activity drop in the daily NRE Labs statistics during his morning routine.

    Remediation
    • removed the liveness probe section from the kubeadm-generated etcd static pod manifest and applied it between etcd restarts
    Action items
    • Add monitoring, especially for the single-node master
    • Run a basic "down for maintenance" page in Google Cloud Functions that points to Twitter for updates, to redirect to during outages
    Lessons

    Because all of the infrastructure is managed as code, the cluster could be rebuilt quickly, but destroying it before finding the cause also destroyed the evidence. Monitoring matters, especially with a single-node master. Read the restart counts in kubectl output, not just the Running status. Remember the fundamentals instead of expecting the issue to be more complicated than it is, and do not let the urgency of an outage push you into hasty decisions. Put up a maintenance page instead of leaving the site failing halfway.

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Check your cluster for this

This case involves etcd and Kubernetes API server. kubegap audits a Kubernetes cluster for gaps like these, read-only, from Claude Code or Codex; its checks cite public reports like the ones in this library.

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By root cause1

unknown1 case

Component
etcdKubernetes API serverkubelet
Contributing factor
Unreviewed defaultsIgnored early signalHarmful manual actionMonitoring blind spotSingle point of failure
Organisation
NRE Labs
  1. IL-0059 Single-master Kubernetes control plane kept dying because the kubelet restarted a healthy etcd on a failing kubeadm liveness probe
    NRE Labs2018