Cases3 cases

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1. IL-0079 A GKE node auto-upgrade to an ubuntu_containerd image with a kernel regression left kube-proxy unable to apply its ip6tables rules, so load balancer health checks failed and several clusters lost all ingress traffic

   Altinity2025

   Symptoms

   On a Saturday, an OpsGenie alert fired for a ClickHouse cluster in Altinity.Cloud that had gone silent: no queries, no metrics, and no logs from customers trying to connect. The pods were running and the nodes looked healthy, but no traffic reached the database. Other clusters soon showed the same thing, and external access was blocked across several GKE clusters.

   Service outage

   Trigger

   GKE automatically upgraded worker nodes to the ubuntu_containerd image 1.32.3-gke.1785003, which ships kernel 6.8.0-1022-gke.

   Root cause

   Breaking change in an upgrade

   Component

   kube-proxyNode operating system imageLinux kernelCloud load balancer

   Contributing factor

   Unpatched known bugNo staged rollout

   Detection

   An OpsGenie alert fired when one ClickHouse cluster stopped receiving queries, metrics and customer connection logs.

   Remediation

   • added maintenance exceptions to pause all upgrades on the GKE clusters that were not yet affected
   • changed the load balancer health check policy to ignore failed kube-proxy health checks, so traffic flowed to the nodes again
   • began migrating the affected clusters from the ubuntu_containerd to the cos_containerd node image by recreating nodes

   Action items

   • Expand image pre-testing pipelines to catch regressions earlier
   • Enable notifications for upcoming GKE auto-upgrades
   • Make GKE maintenance windows required across the fleet to control when upgrades roll out
   • Track Google's issue and wait for a patched Ubuntu image

   Lessons

   A managed node upgrade can break kube-proxy in a way that leaves pods and nodes looking healthy while the load balancer sends nothing, because the load balancer health check depends on kube-proxy. kube-proxy's own logs showed the cause. Altinity recommends that GKE users on ubuntu_containerd restore traffic by switching to externalTrafficPolicy: Cluster, which disables the kube-proxy health check in the load balancer, move production workloads to cos_containerd, and pause auto-upgrades where possible until a patched image has been confirmed and tested.

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2. IL-0230 kube-proxy sync failures during a Kubernetes upgrade corrupted node iptables, and CircleCI jobs stopped starting

   CircleCI2023

   Symptoms

   On 14 March 2023 at about 18:00 UTC, communication errors rose on one CircleCI service, and pipelines for all customers began to start late until jobs did not run at all. Within an hour the errors had spread to many services and to every function of the application, including the CircleCI UI and API.

   Service outageIntermittent connection failuresDNS resolution failures

   Trigger

   At about 17:40 UTC on 14 March the infrastructure team resumed the upgrade of the main production Kubernetes cluster with a changed approach for some components, after a first attempt on 13 March had been rolled back. The ongoing upgrade left kubelet and kube-proxy at mismatched versions.

   Root cause

   Breaking change in an upgrade

   Component

   kube-proxykubeletCoreDNSClient-side DNS resolver and cache

   Contributing factor

   Partial rolloutIneffective rollbackMonitoring blind spotHarmful manual action

   Detection

   At 18:00 UTC engineers saw communication errors rise on one service, then job processing delays climbing and job queues backing up across several services. The kube-proxy "Sync failed" errors were found only in the analysis after the incident.

   Remediation

   • Restarted every node in the cluster so each node built a fresh iptables ruleset
   • Restarted a separate pool of dependencies so jobs using contexts or the machine executor ran again
   • Added capacity to work through the backlog of jobs
   • Restarted the RabbitMQ nodes to fix a few corrupted queues

   Action items

   • Improve the Kubernetes upgrade process to limit the risk of future upgrades
   • Add metrics and alerts for kube-proxy sync errors
   • Evaluate ways to make the RabbitMQ infrastructure more resilient

   Lessons

   No single trigger caused the incident. Because networking underlies everything in the cluster, Kubernetes upgrades carry inherent risk, and CircleCI's risk mitigation did not hold up when several events interacted.

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3. IL-0054 All ingress traffic lost while draining a GKE node pool because the load balancer only targeted new nodes without ingress-nginx pods

   DevOps Hof2019

   Symptoms

   While the old nodes of a GKE cluster were being drained to move workloads to a newly created node pool, none of the services in the cluster could be reached through ingress-nginx any more.

   Service outageProbe failures

   Trigger

   Cordoning and draining the old node pool removed those nodes from the GCP load balancer backend while the ingress-nginx pods were still running on them.

   Root cause

   Operator error

   Component

   Ingress controllerkube-proxyNode pool

   Contributing factor

   Unreviewed defaultsUnverified assumption

   Detection

   The team noticed during the drain that no service in the cluster was reachable through ingress-nginx.

   Remediation

   • deleted the nginx-ingress-controller pods still running on the old nodes so they were rescheduled on the new, ready nodes

   Lessons

   With externalTrafficPolicy: Local, the load balancer can only reach nodes that run an ingress pod, and cordoned nodes leave the load balancer backend immediately; if the ingress pods stay behind on cordoned nodes, all ingress traffic stops. Before any change that might touch traffic, look twice into the documentation.

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