Cases2 cases

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1. IL-0449 Pods on Enigmo's new EKS managed node groups kept restarting or stuck Terminating and the nodes became unusable

   Enigmo2020

   Symptoms

   Two or three days after Enigmo created EKS managed node groups and moved its pods there from the old node groups, the cluster suddenly became unstable: pods restarted again and again or could not stop and stayed around indefinitely, node CPU and memory load rose high, and the nodes became unusable from the cluster.

   Pods stuck in TerminatingSustained high node CPUMemory pressureNode NotReadyUpgrade stall

   Trigger

   Enigmo created EKS managed node groups that used an AMI containing the bug and moved its pods onto them, as preparation for upgrading EKS from 1.15 to 1.16.

   Root cause

   Breaking change in an upgrade

   Component

   Node operating system imageNode pool

   Contributing factor

   Ineffective rollbackChange with a delayed effect

   Remediation

   • Changed the managed node groups' AMI version to the fixed release
   • Ran the managed node group update through CloudFormation
   • Watched the pods across all namespaces during the update
   • Force-deleted every pod that stayed in Terminating with kubectl delete --grace-period=0 --force

   Action items

   • Check the latest releases of the cluster's modules quarterly or monthly and upgrade them regularly

   Lessons

   As long as a team uses Amazon EKS or Kubernetes, it has to keep track of upgrades of the cluster and of modules such as ingress controllers, because a release with breaking changes can be announced without warning after a long stable period. Checking releases and upgrading on a regular schedule keeps the effect of each upgrade on the service small.

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2. IL-0402 mybinder.org launches dropped to zero for hours because a JupyterHub pod on a lost GKE node kept its hub database PVC

   Binder Project2018

   Symptoms

   On 13 March 2018 at 07:28 CET the mybinder.org team noticed that JupyterHub had not been spawning new users and that the launch success rate on the Grafana dashboard had been at zero for several hours. Many pods were in the states "Unknown" and "NodeLost", on at least the nodes `10.128.0.7` and `10.128.0.5`.

   Service outageNode NotReadyPods stuck in TerminatingPods stuck in ContainerCreating

   Root cause

   unknown

   Component

   Persistent volumes and stateful setsNode pool

   Contributing factor

   Pages not delivered

   Detection

   The team noticed only after several hours, when the launch success rate on the Grafana dashboard had been at zero for a long time. No Stackdriver alert email arrived in time, because those emails were marked as spam and reached the team hours later.

   Remediation

   • Cordoned the bad nodes
   • Deleted the hub pod in Unknown state and the hub pod stuck in ContainerCreating
   • Reset node gke-prod-a-ssd-pool-32-134a959a-n2sk from the GCP web interface to force the PVC to be released
   • Force-deleted every pod in Unknown or NodeLost state with kubectl delete --grace-period=0 --force

   Action items

   • Investigate why the outage started, through Stackdriver logs and Google Cloud incidents
   • Set up an alerting service that does not depend on Stackdriver
   • Document how to check whether a PVC has not been released
   • Document how to restart a node by hand when commands are not working
   • Document how to delete pods that are in Unknown state

   Lessons

   The error went unnoticed for a long time because Stackdriver alert emails were marked as spam and arrived hours late. Once the problem was found, each step was logged and the steps were made more forceful as needed, so the hub was down only briefly after detection.

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