Cases3 cases

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1. IL-0018 A Docker Hub password rotation left EKS nodes and Concourse locked out of Docker Hub and unable to pull images

   UK Ministry of Justice2023

   Symptoms

   At 14:22 a Cloud Platform team member noticed failed Docker Hub logins. Fetching an image returned: failed to fetch manifest: Head "https://registry-1.docker.io/v2/ministryofjustice/cloud-platform-tools/manifests/2.1": toomanyrequests: too many failed login attempts for username or IP address

   Image pull failures

   Trigger

   The Docker Hub password was changed as part of LastPass remediation activities while the EKS cluster nodes and Concourse still logged in with the previous password.

   Root cause

   Operator error

   Component

   Container registry and its credentialsNode launch templateNode poolCI system

   Contributing factor

   Credential in configurationShared credential

   Detection

   A Cloud Platform team member saw the failed Docker Hub login error at 14:22. The Kuberhealthy daemonset check showed at 14:52 that the cluster could not pull images, and a user reported ErrImagePull in #ask-cloud-platform at 14:54.

   Remediation

   • Changed the Docker Hub password back to the previous value still used by the EKS cluster nodes and Concourse
   • Confirmed with the reporting user that the pod deployed and that cluster image pulls worked again

   Action items

   • Switch from the Docker Hub username and password to a Docker Hub token created specifically for Cloud Platform
   • Rotate the password cleanly out of hours with a graceful recycle of the nodes

   Lessons

   The write-up states no separate lessons. Its review action replaces the Docker Hub username and password with a Docker Hub token created specifically for Cloud Platform.

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2. IL-0002 CI builder pods could not get AWS IAM credentials because kubelet fell minutes behind its API rate limit

   Zalando2019

   Symptoms

   Builds on Zalando's in-house Continuous Delivery Platform (CDP), which runs CI/CD on Kubernetes, timed out and failed for almost an hour on 11 June 2019. The Kubernetes builder pods could not get AWS IAM credentials.

   High error rateCredentials unavailableControl plane lag

   Trigger

   An unlucky rescaling of the CDP Kubernetes cluster left only one node available for builder pods. Builder pods were created and deleted on that node so quickly that kubelet fell behind.

   Root cause

   Capacity exhaustion

   Component

   kubeletCredential broker for podsKubernetes API serverCI system

   Contributing factor

   Unreviewed defaultsSingle point of failure

   Remediation

   • Scaled the CDP cluster up by hand so builder pods spread over more than one node

   Action items

   • Raise the kubelet QPS limit from the default 5 to 50 in the global cluster configuration

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3. IL-0061 A Terraform pull request merged out of order deleted a production GKE cluster, and recreating it deleted a second one

   Spotify2019

   Symptoms

   Terraform, applied from the shared cluster configuration repository after a merge, deleted Spotify's production GKE cluster in Asia. While the team tried to recreate it, Terraform deleted a second production cluster, so two of the three production clusters were gone.

   Resources deleted

   Trigger

   A feature team's pull request that added three users to an existing RBAC role binding file was merged before the cluster operators' pull request that imported the Asia cluster into Terraform state. The review build of the import pull request had already written the cluster into the shared state file, and the merged configuration had no definition of the Asia cluster, so Terraform removed it.

   Root cause

   Configuration change

   Component

   TerraformCI systemGKE control plane

   Contributing factor

   No safeguard on destructive changeMissed in reviewUnverified assumption

   Detection

   Internal service discovery could not reach the deleted cluster and the cluster operator team was paged.

   Remediation

   • removed the deleted clusters from the service discovery configuration and restarted service discovery so clients fell back to the instances outside Kubernetes
   • one team that ran half on Kubernetes and half on VMs created more VMs outside Kubernetes to handle the load
   • recreated the clusters, using the hourly backups
   • updated the places where the old clusters' master IPs were hardcoded

   Action items

   • Post the Terraform dry-run output as a comment on each pull request
   • Require a status check that the branch is up to date with master, so the dry run reflects what will actually happen
   • Require an approving review on pull requests
   • Fail reviews automatically when certain keywords such as destroy appear; cluster deletions are done manually outside this repository
   • Add linters and validators for the cluster configuration
   • Schedule and announce disaster recovery tests that cover a cluster going away and smaller failures

   Lessons

   Plan for failure from the start and migrate large infrastructure gradually, so there is redundancy and a way back. A backup whose restore has never been tested is not a backup. Practising disaster recovery paid off: restoring the first deleted cluster took three and a quarter hours, and the team can now restore a larger cluster in one hour. What matters is not who made the mistake but what was learned from it.

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