Cases3 cases

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1. IL-0087 After a cold reboot of RKE2 nodes, pods could not get IP addresses because Multus could not reach the Kubernetes API, and further reboots spread the failure to every node

   Fyra Labs2023

   Symptoms

   At around 2 AM ICT on 2023-04-09 the team saw unusual CPU use on one cluster node, which throttled every other service on it and made them fail. They presumed an upstream container runtime bug in containerd and runc and decided to fully reboot the affected nodes, taking the cluster down for maintenance on the assumption that it was not in active use.

   Sustained high node CPUService outage

   Trigger

   A full cold reboot of the nodes that showed unusual CPU use, followed by upgrades and cold reboots of the other nodes.

   Root cause

   unknown

   Component

   Multus meta-CNICalicoContainer runtime

   Contributing factor

   Harmful manual actionUnverified assumption

   Detection

   The team saw unusual CPU use on a node around 2 AM ICT and failing services on the rebooted nodes around 2:30 ICT; developers reported the Terra repositories down at 6:31 ICT.

   Remediation

   • uninstalled Multus and Calico and replaced them with the Cilium CNI
   • rolled back most cluster settings except the CNI

   Lessons

   Rebooting nodes to clear one problem can expose another; here a CNI chain could not reach the API server after a cold start. Repeating the same reboot on more nodes while the first failure was not understood spread the outage from a few nodes to the whole cluster. The team also found that Cilium's real resource use in their cluster was acceptable, contrary to the benchmark they had relied on.

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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-0086 A deployment meant for a CircleCI test Kubernetes cluster also removed Traefik and Calico resources from the production cluster, taking down the CircleCI UI and runner.circleci.com

   CircleCI2021

   Symptoms

   At 15:35 EST on 11 March 2021 the CircleCI web UI and runner.circleci.com became unavailable. The API, which uses a separate ingress point, stayed reachable, and builds kept running.

   Service outageResources deleted

   Trigger

   An update deployed to a test Kubernetes cluster also removed Traefik and Calico resources from CircleCI's primary production cluster.

   Root cause

   Faulty deployment

   Component

   Ingress controllerCalico

   Contributing factor

   Excessive blast radiusNo runbookMonitoring blind spot

   Detection

   CircleCI engineers were alerted and began investigating. The status page posted its first notice at 20:45 UTC.

   Remediation

   • restored Traefik in the production cluster
   • restored Calico in the production cluster, after which pods served customer requests again

   Action items

   • Improve network-level documentation and runbooks to cover every layer of the Kubernetes networks
   • Improve monitoring and alerting for the network infrastructure
   • Add guardrails that isolate the production and staging clusters so they cannot interfere with each other

   Lessons

   A deployment path that can reach both a test cluster and production can remove shared networking components from production. When the ingress controller and the CNI are both affected, restoring the ingress alone is not enough: engineers had to find the link between Calico and Traefik and restore Calico before pods served traffic again. Time went to DNS and AWS red herrings because nothing linked the outage to the test deployment; CircleCI's answer is better network runbooks, network alerting and guardrails between clusters.

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