Cases3 cases

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1. IL-0180 A GKE control plane auto-upgrade from 1.22 to 1.23 removed the v1beta1 Ingress and ValidatingWebhookConfiguration APIs that Istio 1.7.4 still used, and Istio stopped working in production

   Sunwoo Park2023

   Symptoms

   On 2023-05-18 a Slack alert arrived at 20:01 and Istio stopped working properly in the production GKE cluster. The istiod error logs said that the v1beta1.Ingress and v1beta1.ValidatingWebhookConfiguration resources could not be found.

   Service outage

   Trigger

   GKE automatically upgraded the production cluster's control plane from 1.22.17-gke.7500 to 1.23.17-gke.1700 at 19:52 on 2023-05-18.

   Root cause

   Breaking change in an upgrade

   Component

   IstioGKE control planeAdmission webhook

   Contributing factor

   Deferred upgrades

   Detection

   A Slack alert at 20:01 on 2023-05-18, nine minutes after the control plane upgrade. The istiod error logs showed that the v1beta1 Ingress and ValidatingWebhookConfiguration resources could not be found.

   Remediation

   • upgraded Istio from 1.7.4 to 1.13.3

   Lessons

   The first diagnosis, end of support for Istio, was wrong; the real cause was found by matching the alert time against the cluster's UPGRADE_MASTER operations in Logs Explorer. The author recommends checking the version compatibility matrices of Kubernetes, Istio and other packages, keeping a production version for at least six months and upgrading three months before end of support, keeping the test environment on the latest version, backing up before upgrades, managing deployments and versions with a tool such as Argo CD, and testing upgrades in a test environment before production.

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2. 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.

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3. IL-0090 After an upgrade of the ModSec ingress controller module, its validating webhook served a certificate for the wrong service name and blocked every Ingress create and change

   UK Ministry of Justice2021

   Symptoms

   At 13:15 on 9 June 2021 a user reported in the #ask-cloud-platform channel that deploying a UAT application failed on its Ingress resource.

   Deploys failing

   Trigger

   The Cloud Platform team upgraded the ModSec ingress controller module to v3.33.0; the deployment appeared to succeed.

   Root cause

   Breaking change in an upgrade

   Component

   Admission webhookIngress controller

   Contributing factor

   Unrepresentative staging

   Detection

   A user reported the deployment error in the #ask-cloud-platform Slack channel at 13:15.

   Remediation

   • rolled back the ModSec ingress controller module to v0.0.7

   Action items

   • Find out why the issue was not flagged in the test cluster and try to reproduce it, possibly with a new test (ticket #2972)
   • Add a smoke test that checks the alerts in Alertmanager (ticket #2973)
   • Add a helloworld app that uses the ModSec controller so smoke tests can check that traffic works (ticket #2974)
   • Make a new version of the ModSec module work on EKS for both live-1 and live; neither the old nor the new version works on live (ticket #2975)

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