Cases2 cases

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1. IL-0101 After Google forced a GKE control plane upgrade to 1.33.2 at a deprecation deadline, no new node could initialise, so autoscaling and spot node replacement stopped for 15 hours

   Wealthy2025sev1

   Symptoms

   Nodes that already existed kept running, but every new node, spot or standard, on either v1.32 or v1.33, failed to initialise and could not join the cluster. Spot nodes that were preempted and recreated never came back, so services degraded progressively: background workers on spot instances, reporting services and order allocation stopped completely, and the APIs on existing nodes kept answering but could not scale for load spikes.

   Scale-up failureContainer crash loopService outageDNS resolution failures

   Trigger

   Google upgraded the GKE control plane from v1.32.x to v1.33.2 at the version deprecation deadline, although auto-upgrade was disabled on the node pools.

   Root cause

   Breaking change in an upgrade

   Component

   GKE control planeNode poolClient-side DNS resolver and cachePersistent volumes and stateful setsConfigMaps and Secrets

   Contributing factor

   Deferred upgradesSingle point of failureIneffective rollbackNo headroom

   Remediation

   • Created a new GKE cluster at v1.33, the version of the forced upgrade
   • Upgraded Istio to 1.27.1 for Kubernetes 1.33 compatibility
   • Updated the cert-manager configuration for Kubernetes 1.33
   • Migrated all production workloads to the new cluster and verified pod scheduling, DNS resolution, PVC mounting and external integrations
   • Decommissioned the broken cluster

   Action items

   • Configure all clusters to use the GKE stable release channel
   • Implement a separate management cluster for Argo CD, monitoring and other control components (Q4 2025)
   • Review spot instance usage for critical workloads and add on-demand fallback pools
   • Document the SRE upgrade procedure: management cluster first, production after a monitoring period of several days
   • Document a Kubernetes, Istio and cert-manager compatibility matrix
   • Create an automated upgrade testing pipeline
   • Reserve static IPs for quick migrations
   • Pin versions of Istio, cert-manager, CSI and DNS addons
   • Stay current with stable releases and regularly check GKE alerts and announcements to avoid deprecation deadlines

   Lessons

   GKE upgrades the control plane at a version's deprecation deadline even when auto-upgrade is disabled, so staying inside the supported version window is how to avoid a forced upgrade. A control plane upgrade can leave existing nodes healthy while every new node fails, and spot nodes that cannot rejoin after preemption turn this into cascading failures. Relying heavily on spot instances for critical workers turned a node join failure into a progressive outage. Kubernetes upgrades have to be planned together with dependent components such as Istio and cert-manager, and without a standby cluster on the same provider there was no immediate failover; the only recovery left was building a new cluster.

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2. IL-0107 Kyverno stuck in a crash loop behind a webhook with failurePolicy fail blocked every change to Kubernetes Service objects for 88 minutes

   DFDS2022

   Symptoms

   At 11:38 UTC on 3 August 2022 an end-user team told the platform team that applying a Service resource to one of the Kubernetes clusters failed.

   Deploys failingContainer crash loop

   Trigger

   A certificate chain in a third-party application expired, through no action of DFDS, and the outdated Kyverno installation got stuck in a crash loop.

   Root cause

   Certificate or credential expiry

   Component

   Policy engineAdmission webhook

   Contributing factor

   Deferred upgradesUnreviewed defaultsMonitoring blind spotIgnored early signal

   Detection

   An end-user team alerted the platform team at 11:38 UTC that applying a Service resource failed; the platform team started looking into it at 11:50 UTC.

   Remediation

   • reproduced the issue in a sandbox cluster and deployed the fix there first
   • updated Kyverno to a newer Helm chart version in the affected production cluster

   Action items

   • Implement monitoring on Kyverno
   • Create internal documentation on the Kyverno setup
   • Investigate the exact certificate issue in the third-party application
   • Consider changing the failurePolicy on ClusterPolicy resources going forward

   Lessons

   Operational issues should be added to the 'Ops Day to Day' board from the start.

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