Cases2 cases

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1. IL-0244 A queued pull request destroyed the EKS subnet route table associations and Cloud Platform services went offline

   UK Ministry of Justice2024

   Symptoms

   On 20 September 2024 at 11:24 the Cloud Platform team received high priority Pingdom alerts for services on the live cluster, and from 11:26 teams reported in the #ask channel that services were unavailable. Users reported that services could not be resolved.

   Service outageNetwork unreachableResources deleted

   Trigger

   At 11:21 the infrastructure-vpc-live-1 pipeline was unpaused, and a pull request that had been waiting in its queue ran automatically.

   Root cause

   Operator error

   Component

   TerraformCI systemVPC route tables and firewall rules

   Contributing factor

   No safeguard on destructive change

   Detection

   High priority Pingdom alerts for live cluster services reached the Cloud Platform team at 11:24, and users reported that services could not be resolved.

   Remediation

   • Ran terraform apply locally to rebuild the subnet route table associations

   Action items

   • Review and update the process for pausing and resuming infrastructure pipelines so every team member knows its implications
   • Find a way to hold queued pull requests while manual infrastructure updates are under way
   • Find ways to isolate the plan and apply tasks of infrastructure pipelines better

   View case
2. IL-0473 Jenkins infrastructure went fully down after a pod IP range fix deleted every AKS node pool and could not recreate them

   Jenkins project2023

   Symptoms

   On 7 July 2023 from 11:05 to 15:25 UTC many public Jenkins infrastructure services were completely down, including get.jenkins.io, plugins.jenkins.io, accounts.jenkins.io, javadoc.jenkins.io and incrementals.jenkins.io, while ci.jenkins.io, issues.jenkins.io, repo.jenkins-ci.org and www.jenkins.io were partly or completely disrupted.

   Network unreachableResources deletedCluster or node provisioning stallService outage

   Trigger

   After the upgrade to Kubernetes 1.25 changed the range of the pods' originating IP and LDAP access was blocked, a fix (Azure PR 431) deployed at 10:55 UTC to set a proper set of pod IP ranges removed all node pools of the cluster.

   Root cause

   Configuration change

   Component

   Node poolCNI pluginCloud load balancer

   Contributing factor

   Unverified assumptionNo staged rolloutNo safeguard on destructive change

   Detection

   After the upgrade, at 10:30 UTC, the team noticed that services inside the cluster, such as accounts.jenkins.io, could not reach the LDAP service.

   Remediation

   • Created the cluster again from scratch with a fixed network setup
   • Set a custom pod CIDR in a range separate from the virtual network
   • Moved the services and their DNS records to new public IPs
   • Pushed a pull request that recorded the manual rebuild, including the IP setup, in code

   Action items

   • Protect the public IPs from deletion with a Management Lock
   • Keep the public IPs in a separate resource group and point the Kubernetes-managed load balancers to it with the service.beta.kubernetes.io/azure-load-balancer-resource-group annotation
   • Improve network diagrams and documentation so possible overlaps are visible when preparing operations
   • Avoid changing the configuration of all AKS node pools at once

   Lessons

   The team said that changing one node pool at a time would have shown the problem after the first pool and avoided a full outage, and that the public IPs should change as little as possible because users behind corporate firewalls with allow-lists depend on them. The team also noted that it could rebuild, in under 4 hours, the cluster that hosts almost all public services.

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