Cases5 cases

1 to 5 of 5

1. IL-0095 An engineer deleted the prod namespace of the LEAP JupyterHub while believing the kubeconfig pointed at a new cluster, and the hub was down for about an hour

   2i2c2025

   Symptoms

   At 5:00 PM BST on 12 August 2025 a 2i2c engineer declared an incident. While deploying a new cluster called temple and running into NFS issues, the engineer had deleted the prod namespace; the deletion hung, and listing the pods showed many users from a different cluster. The engineer's first message suggested that the kubeconfig had somehow been mutated or corrupted and that some other cluster was being torn down.

   Resources deletedService outage

   Trigger

   While working around a bug in the NFS deployment process for a new hub, an engineer ran a delete of the prod namespace with the kubeconfig context pointing at the LEAP cluster.

   Root cause

   Operator error

   Component

   Persistent volumes and stateful setsJobs and CronJobsIngress controllerTerraform

   Contributing factor

   No safeguard on destructive changeNo runbook

   Detection

   The engineer who ran the deletion noticed when it hung and the pod list showed users of another cluster, and declared the incident at 5:00 PM BST, before the uptime check on leap.2i2c.cloud failed at 5:32 PM.

   Remediation

   • deleted the single remaining user pod in prod so the namespace deletion completed
   • killed the nfs-share-creator job that was blocking the deployment
   • redeployed the prod hub with the updated NFS server IP address
   • deleted the prod ingress during the deployment so that users could not start servers mid-deployment

   Action items

   • Write an incident report
   • Write a short incident response document for the case "I deleted prod, what next?"
   • Upgrade jupyterhub-home-nfs and remove the nfs-share-creator job
   • Add opt-in hardening against nested kubeconfig contexts to the deployer system
   • Change the engineer's shell configuration to show distinct kubeconfig contexts more clearly

   Lessons

   Provisioning persistent storage outside Kubernetes with Terraform meant a deleted namespace cost an hour of downtime and no data. The engineer had no visible cue for which kubeconfig context was active, which turned a workaround on a new cluster into a deletion on a production one. The engineer knew the fix but did not feel confident redeploying without first confirming with the tech lead, in another time zone, that there was no risk of losing persistent data, and reaching the tech lead took time.

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2. IL-0078 Enabling EKS secrets encryption with KMS through Terraform removed worker node IAM permissions and took down all ZenML Pro workspaces

   ZenML2025

   Symptoms

   Between 12 AM and 8 AM CEST on 11 May 2025, every ZenML Pro workspace server was unreachable, so customers could not use workspace UIs or pipelines. The ZenML Pro dashboard was not affected.

   Service outage

   Trigger

   At 23:38 on 10 May, secrets encryption with AWS KMS was enabled through Terraform as part of the EKS module upgrade.

   Root cause

   Software defect

   Component

   TerraformNode pool

   Contributing factor

   Unrepresentative stagingDeferred upgrades

   Detection

   Engineers found the cluster degraded when they resumed the upgrade at 06:00.

   Remediation

   • deleted and recreated the EKS node group with the correct IAM permissions and configuration
   • restored service access across all affected ZenML Pro environments

   Action items

   • Upgrade all Terraform modules (EKS, VPC) to current supported versions
   • Complete the EKS cluster upgrades as planned
   • Review the strategy for periodic Kubernetes and infrastructure upgrades to prevent a recurrence

   Lessons

   A successful upgrade on a much smaller staging cluster understated the risk of the same change in production. Skipping Kubernetes and module versions let upgrade complexity build up until one upgrade carried many changes at once.

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3. IL-0091 Changing the worker node instance type through Terraform recycled all nodes at once and deleted users' production pods together

   UK Ministry of Justice2023

   Symptoms

   At 10:23 on 6 June 2023 a user of the Cloud Platform reported that all of their production pods had been deleted at the same moment. Several users received Pingdom alerts that their applications were down for a few minutes.

   Service outage

   Trigger

   The team changed the instance type of the cluster's worker nodes through Terraform.

   Root cause

   Configuration change

   Component

   Node poolTerraform

   Contributing factor

   Excessive blast radiusNo runbook

   Detection

   Users reported that their production pods had been deleted at once and that Pingdom alerts showed their applications down; the incident was declared at 11:00.

   Action items

   • Ask AWS, through a support ticket, for the steps to change the node instance type without an outage
   • Plan how to make instance type changes through Terraform without downtime and add a runbook with the steps for changing the node instance type

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4. IL-0109 A retried node rollover on a DFDS EKS cluster set the Auto Scaling group back to 15 instances, and the default termination policy removed every healthy worker node, leaving the cluster with no nodes

   DFDS2023sev1

   Symptoms

   At 09:33 UTC on 14 February 2023 end users told the platform team that Kubernetes logs were not arriving in CloudWatch as expected. The investigation went through fluentd and found that the nodes were running containerd as their container runtime instead of docker-shim. A scheduled node rollover the day before, at 07:30 UTC on 13 February, had set containerd as the default runtime by accident.

   Service outageResources deletedMonitoring outage

   Trigger

   A scheduled node rollover had accidentally made containerd the default container runtime, which stopped log shipping to CloudWatch; the unscheduled rollover to revert it timed out, and the pipeline run that followed reduced the Auto Scaling group from 30 to 15 instances.

   Root cause

   Configuration change

   Component

   Container runtimeNode launch templateNode poolTerraformTelemetry agent

   Contributing factor

   Automation amplificationUnreviewed defaultsUnrepresentative stagingNo configuration testsNo runbookHarmful manual action

   Detection

   End users reported the missing CloudWatch logs that started the work. The postmortem lists 2 minutes as the time to detection of the node failure.

   Remediation

   • ran the node rollover script to add new nodes, which failed on a timeout from Docker Hub
   • ran the node rollover script a second time, which added new nodes that the load balancer marked healthy at 11:01 UTC

   Action items

   • Document the rollover process, especially what can be done when it goes wrong
   • Investigate options for improving the rollover process
   • Add fluentd log collection to the QA test suite so logs are covered end to end
   • Add alarms for fluentd when too little or no log data is sent
   • Implement a staging environment
   • Implement guards against selecting an invalid container runtime

   Lessons

   When a change goes wrong, rolling back to a known working configuration is safer than rushing a fix, which can make the damage worse. Launching new worker nodes depends on the cloud-init script not failing in any way. The QA configuration differed from production, there was no staging environment, the QA tests did not cover fluentd log collection, and the rollover process had no documentation for when it fails.

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5. IL-0105 Replacing the AWS VPC CNI during a Terraform refactoring detached the ALB target groups, and every service in the Kubernetes cluster returned 503

   DFDS2021

   Symptoms

   At 08:29 UTC on 22 June 2021 alerts fired because all services in the Kubernetes cluster were returning 503. No inbound traffic was reaching the cluster. A customer reported the problem at 08:32.

   Service outageHigh error rate

   Trigger

   The pipeline replaced the AWS VPC CNI as part of a refactoring that moved EKS add-ons from kubectl to native Terraform management.

   Root cause

   Configuration change

   Component

   AWS VPC CNICloud load balancerTerraform

   Contributing factor

   Unverified assumptionNo configuration tests

   Detection

   Alerts fired at 08:29 UTC, eight minutes after the VPC CNI was replaced; a customer reported the issue at 08:32.

   Remediation

   • committed a fix that reverted the infrastructure-modules reference
   • re-triggered the pipeline after it failed on an AWS API timeout
   • let the pipeline reattach the target groups to the ALB

   Action items

   • Revert the ALB de-registration delay to the default of 300 seconds
   • Update the roll-over script to set the ALB de-registration delay to zero temporarily before a roll-over
   • Create an ingress test suite

   Lessons

   The change to the de-registration delay had been weighed mainly for performance. Critical pipeline runs should be watched while they run. Everyone should receive the alerts and react to them, and alert messages that were unclear should be reworded.

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