Incident Library
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Cases2 cases

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  1. IL-0060 Kubernetes 1.24 upgrade removed the master node label that Calico route reflectors selected on, dropping all pod routes and taking Reddit down for 314 minutes
    Reddit2023
    Symptoms

    About two minutes after an engineer started the Kubernetes 1.23 to 1.24 upgrade of the cluster running Reddit's legacy stack, just after 19:00 UTC, the site stopped. The CDN edge request graph, which is kept separate from the cluster, showed traffic by status collapsing. Users saw the error page, a homepage with no posts, or plain errors.

    Service outageHigh error rateDNS resolution failuresMonitoring outagePods stuck in ContainerCreatingControl plane lag
    Trigger

    An in-place upgrade of the legacy cluster from Kubernetes 1.23 to 1.24; in 1.24 the node-role.kubernetes.io/master label is removed even from running clusters.

    Root cause
    Breaking change in an upgrade
    Component
    CalicoKubernetes API serverAdmission webhooketcd
    Contributing factor
    Configuration not in codeUnrepresentative stagingUntested backupMonitoring blind spotSingle point of failure
    Detection

    The site broke about two minutes into the upgrade; an incident was opened immediately and responders were on the call within three minutes, working from CDN edge graphs because the cluster's own metrics were gone.

    Remediation
    • deleted the Open Policy Agent webhook configurations to stop API server timeouts
    • terminated all worker nodes of the cluster
    • restored the control plane from the pre-upgrade backup onto the first control plane node
    • switched off the cluster autoscaler until the control plane was stable
    • generated new TLS certificates so replacement control plane nodes could join etcd
    • brought traffic back in steps from 1% to 100%
    • restarted legacy services that had been stopped by hand
    Action items
    • Codify cluster configuration so every choice has a record, and document in detail what cannot be codified
    • Standardise components across clusters and replace bespoke configurations
    • Build tooling to manage the lifecycle of whole clusters so they can be recreated or replicated
    • Add pre-production clusters that can be tested with confidence
    • Improve the backup restore process and make cluster upgrades safe
    Lessons

    Configuration that exists only in a live cluster, edited by hand through a special tool, can be forgotten, as the route reflector setup was, and then break on an upgrade nobody connects it to. A Kubernetes upgrade cannot be reverted without a restore, so the restore procedure has to be kept current and practised. Consistent, codified clusters are what make upgrades testable; bespoke clusters keep producing outages.

    View case
  2. IL-0521 AKS pods could not mount volumes and new nodes got no CNI network interface after the cluster service principal expired
    Jenkins project2021
    Symptoms

    From 18:02 UTC on 2 June 2021, the Jenkins infrastructure AKS cluster logged errors about pods that were unable to mount volumes and about scaled-up nodes that were unable to obtain a network virtual interface from the CNI.

    Credentials unavailablePods stuck in ContainerCreating
    Trigger

    The Azure Service Principal credential of the AKS cluster expired at 17:53 UTC on 2 June 2021.

    Root cause
    Certificate or credential expiry
    Component
    Cluster cloud identityPersistent volumes and stateful setsCNI pluginNode pool
    Contributing factor
    Monitoring blind spot
    Detection

    The error behind the failures was found in the AKS UI console while the team investigated the root cause of the LTS 2.289.1 release problem.

    Remediation
    • Renewed the AKS cluster's Azure Service Principal credential, which made AKS restart all nodes automatically
    Action items
    • Add an automatic PagerDuty check that alerts a week before the service principal expires, as is done for certificates
    • Keep a team-level calendar for manual operations such as resetting a credential
    • Consider managed identities, which renew automatically, instead of the service principal
    View case
Check your cluster for this

These 2 cases involve Admission webhook and Calico. 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 cause2

Breaking change in an upgrade1 case

Component
Admission webhookCalicoetcdKubernetes API server
Contributing factor
Untested backupConfiguration not in codeMonitoring blind spotSingle point of failureUnrepresentative staging
Organisation
Reddit
  1. IL-0060 Kubernetes 1.24 upgrade removed the master node label that Calico route reflectors selected on, dropping all pod routes and taking Reddit down for 314 minutes
    Reddit2023

Certificate or credential expiry1 case

Component
Cluster cloud identityCNI pluginNode poolPersistent volumes and stateful sets
Contributing factor
Monitoring blind spot
Organisation
Jenkins project
  1. IL-0521 AKS pods could not mount volumes and new nodes got no CNI network interface after the cluster service principal expired
    Jenkins project2021