Incident Library
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Cases6 cases

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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

These 6 cases involve Kubernetes API server and etcd. 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 cause5

Dependency failure1 case

Component
Cloud block storageData center power and coolingetcdInfiniBand fabric
Contributing factor
Monitoring blind spotNo alert on limitNo runbookOverlapping failuresSingle point of failure
Organisation
Nebius
  1. IL-0133 A storm shut down cooling at Nebius's us-central1 data center, and a disk hot-plug bug kept Managed Kubernetes control planes down for hours after power returned
    Nebius2026

Software defect1 case

Component
GPU driverKubernetes API serverLinux kernel
Contributing factor
Change with a delayed effectIgnored early signalMonitoring blind spotSingle point of failure
Organisation
Barush Mendez
  1. IL-0138 A failed Nvidia driver build left broken kernel packages on the only Kubernetes master node, which hit a kernel panic on reboot after a power outage and took the homelab cluster down for six days
    Barush Mendez2025

Configuration change2 cases

Component
Kubernetes API server2Admission webhook1Client-side DNS resolver and cache1GKE control plane1kubelet1Telemetry agent1
Contributing factor
Monitoring blind spot2Automation amplification1Excessive blast radius1Cache-masked failure1Limited debug access1No health probes1No staged rollout1Unrepresentative staging1
Organisation
Jetstack1OpenAI1
  1. IL-0005 A new telemetry service overloaded the Kubernetes API servers of large clusters and broke DNS-based service discovery for all OpenAI services
    OpenAI2024
  2. IL-0008 An unresponsive OPA validating webhook crash-looped the API server during a GKE master upgrade, and node auto-repair then recreated every node
    Jetstack2019

Capacity exhaustion1 case

Component
etcdKubernetes API serverTelemetry agent
Contributing factor
Unverified assumptionUnknown limitMonitoring blind spotNo capacity planning
Organisation
Civis Analytics
  1. IL-0075 Kubernetes API servers pegged on CPU when the cluster grew to about 290 nodes, traced to Datadog agents polling the API
    Civis Analytics2019

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