Incident Library
Applied filters Root causeBreaking change in an upgradeFactorUnverified assumptionDomainKubernetesClear allEvery case under the filters, with no sentence; newest first.
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Cases2 cases

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  1. IL-0097 A cluster autoscaler version bump was incompatible with the one cluster still on Kubernetes 1.33, so no scale-up events fired and new nodes were not created
    2i2c2026
    Symptoms

    At 15:10 (Bucharest time) on 2026-03-31 an alert fired for the prod hub on the berkeley-geojupyter cluster on AWS: "[FIRING:1] At least two servers failed to start in the last 30m cluster=berkeley-geojupyter hub=prod (provider=aws immediate action needed)". It opened PagerDuty incident #2057.

    Scale-up failure
    Trigger

    An upgrade merged on 2026-03-30 bumped the cluster autoscaler version, and the new version was incompatible with Kubernetes 1.33, which the berkeley-geojupyter cluster still ran.

    Root cause
    Breaking change in an upgrade
    Component
    Cluster autoscaler
    Contributing factor
    Deferred upgradesUnverified assumption
    Detection

    An alert that at least two servers failed to start in the last 30 minutes fired at 15:10 and opened PagerDuty incident #2057. The report notes it was triggered by an automatic health check run, not by users being unable to start servers.

    Remediation
    • upgraded the cluster's Kubernetes version from 1.33 to 1.34
    • downgraded the cluster autoscaler by one patch version to 9.55.0, the version meant for Kubernetes 1.34
    Action items
    • The change in https://github.com/2i2c-org/infrastructure/pull/8008 (the report gives only the link)
    • Use recurrent issues, such as the recurrent-k8s-aws-upgrades workflow, to standardize Kubernetes versions across clusters
    Lessons

    Because the context of the autoscaler bump was fresh, the team went down the right path from the start. The upgrade batches had been designed with only 1.32 clusters in mind, so the one 1.33 cluster was missed and got an incompatible autoscaler. 2i2c notes it was lucky that an automatic health check, not real users, hit the failure first.

    View case
  2. IL-0522 An ingress-nginx chart upgrade deleted the jenkins.io Ingress and Fastly served HTTP/503 errors for hours
    Jenkins project2021
    Symptoms

    At 11:32 UTC on 18 November 2021, a user reported in the jenkinsci/jenkins Gitter channel that https://www.jenkins.io/doc/pipeline/steps/ was answering HTTP/503 errors with the message "Guru meditation" from Fastly's varnish.

    Service outageResources deleted
    Trigger

    The ingress-nginx Helm chart was upgraded from 4.0.6 to 4.0.8 at 10:42 UTC, and the new chart added an admission webhook rule that forbids Nginx configuration blocks in Ingress annotations.

    Root cause
    Breaking change in an upgrade
    Component
    Ingress controllerAdmission webhookHelmCDN and edge network
    Contributing factor
    Unverified assumptionCache-masked failureMonitoring blind spotHarmful manual action
    Detection

    A user reported in the jenkinsci/jenkins Gitter channel at 11:32 UTC that a jenkins.io page answered HTTP/503 errors, and status.jenkins.io reported the incident at 11:49 UTC.

    Remediation
    • Disabled the automated systems, rolled the ingress-nginx chart back to 4.0.6 and deleted the admission webhook by hand
    • Removed the forbidden annotations from the jenkins.io configuration
    • Upgraded the jenkins.io Helm chart to the last version known to work with ingress-nginx 4.0.8
    • Redeployed the jenkins.io Helm chart through the automated system and told Fastly to drop all cached pages
    Action items
    • Always read the changelog in depth when updating the ingress controllers, with two people pairing in real time
    • Add custom Datadog monitoring for www.origin.jenkins.io so that such an outage is detected
    • Make the monitor send the Host header www.jenkins.io so it is not redirected to Fastly
    • Check a set of pages, such as the pipeline steps page, not only the front page
    • Consider an ephemeral k3s end-to-end test before deploying to production
    Lessons

    Trusting a patch version of a Helm chart for the Ingress controller without reading its changelog in depth let a new admission rule remove the jenkins.io Ingress in production. Without monitoring on origin.jenkins.io, a user found the outage. A complete staging cluster with the same DNS setup would have caught the problem before production.

    View case
Check your cluster for this

These 2 cases involve Admission webhook and CDN and edge network. 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

Breaking change in an upgrade2 cases

Component
Admission webhook1CDN and edge network1Cluster autoscaler1Helm1Ingress controller1
Contributing factor
Unverified assumption2Cache-masked failure1Harmful manual action1Monitoring blind spot1Deferred upgrades1
Organisation
2i2c1Jenkins project1
  1. IL-0097 A cluster autoscaler version bump was incompatible with the one cluster still on Kubernetes 1.33, so no scale-up events fired and new nodes were not created
    2i2c2026
  2. IL-0522 An ingress-nginx chart upgrade deleted the jenkins.io Ingress and Fastly served HTTP/503 errors for hours
    Jenkins project2021