Cases3 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-0185 A disk failure made the first control plane node of a Kubespray cluster read-only, and recovery needed the Kubespray inventory reordered and a new control plane node joined

   Hans H. Kim2023

   Symptoms

   The kernel on a master node of the Kubernetes cluster logged disk I/O errors: "[HAWKEYE] kernel:: [22329228.540857] blk_update_request: I/O error, dev sda, sector 795030104 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0". The sda disk switched to read-only, and the machine needed a new disk and an operating system reinstall.

   Node NotReady

   Trigger

   A hardware failure of the disk on the first control plane node.

   Root cause

   Hardware failure

   Component

   KubesprayetcdNode root diskConfigMaps and Secrets

   Contributing factor

   Single point of failure

   Detection

   Disk I/O errors from blk_update_request on dev sda appeared in the node's kernel log.

   Remediation

   • reordered the kube_control_plane group in the Kubespray inventory so that node-2 became the first control plane node
   • removed the failed machine from the cluster
   • edited the cluster-info ConfigMap in kube-public to point at a live control plane node and updated certificate-authority-data
   • installed and configured kubelet and the other components on a new node and joined it as a control plane node with kubeadm, skipping the etcd join phase
   • added the etcd member separately

   Lessons

   In a Kubespray cluster the first node of the kube_control_plane inventory group is special, so its failure needs its own procedure: move another node into the first position, fix the cluster-info ConfigMap, join a new control plane node and add the etcd member back. etcd should be brought back to full membership before another control plane node fails.

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3. IL-0066 Broken ConfigMap change lay dormant for weeks, then took down Pusher's edge proxy when a cluster upgrade replaced its pods

   Pusher2019

   Symptoms

   During a cluster upgrade, all traffic to Pusher's products stopped. The speaker recalls that requests were failing with 500 errors.

   Service outageHigh error rate

   Trigger

   A cluster upgrade replaced nodes, so the bridge pods restarted and loaded a ConfigMap that had been changed three or four weeks earlier.

   Root cause

   Configuration change

   Component

   ConfigMaps and Secrets

   Contributing factor

   Change with a delayed effectUnverified assumption

   Action items

   • Build and run Wave so that changes to ConfigMaps and Secrets roll out new pods immediately

   Lessons

   A ConfigMap change does not restart the pods that use it, so for an application that cannot reload its configuration the change takes effect only when pods are next replaced, possibly weeks later during unrelated work. Tie configuration to the pod template so a bad change fails at the moment it is made.

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