Cases2 cases

1 to 2 of 2

1. IL-0112 The daily node rollover put DFDS's EKS nodes on an AMI later recalled for a kernel issue, causing "PLEG is not healthy" NodeNotReady flaps and pod network timeouts

   DFDS2022

   Symptoms

   On 2022-10-31 a planned upgrade of the vpc-cni EKS add-on, started from the deployment pipeline at 13:45 UTC, timed out at 14:10. Only about 10 of the 45 aws-node pods had upgraded, 5 were stuck in Terminating and the other 30 had not been attempted.

   Node NotReadyUpgrade stallIntermittent timeoutsIntermittent connection failures

   Trigger

   At 07:30 UTC on 2022-10-31 the daily node rollover replaced the existing nodes with nodes built from AMI v20221027, the latest AWS EKS node AMI, released on 2022-10-29 and later recalled because of a kernel issue.

   Root cause

   Software defect

   Component

   Node operating system imageLinux kernelkubeletAWS VPC CNINode launch templateTerraform

   Contributing factor

   No staged rolloutAutomation amplificationOverlapping failuresMonitoring blind spotNo health probes

   Detection

   The team noticed nodes flapping between NodeNotReady and NodeReady ("KubeletNotReady PLEG is not healthy") at 14:30 UTC while watching the stalled vpc-cni upgrade, about seven hours after the rollover. Time to detection was 7 hours. Alerting did not catch the NodeNotReady events or the socket growth.

   Remediation

   • cordoned, drained and deleted 15 stuck nodes one at a time to complete the vpc-cni upgrade
   • changed the Terraform infrastructure-modules so a specific AMI could be set
   • rolled the EC2 Auto Scaling group launch configuration back to the previous known good AMI through the pipeline

   Action items

   • Reach out to teams with suggestions about readiness and liveness probes
   • Create a dashboard for readiness and liveness probe coverage
   • Write a wiki article on readiness and liveness probes and their usefulness
   • Modify infrastructure-modules to allow specifying a particular AMI
   • Schedule a discussion on whether to take the latest AMI immediately and how to test new AMIs before they are deployed
   • Implement alerting on abnormal NodeNotReady events and on increased socket use
   • Create a learning path for Kubernetes within the team
   • Collect logs from nodes centrally
   • Create a Prometheus exporter that retrieves the latest available AMI, with a dashboard and alerts

   Lessons

   When a new node AMI has just been rolled out, upgrading other cluster components on the same day makes it hard to tell which change is causing trouble; here the vpc-cni upgrade on the same day confused matters. Taking the latest AMI automatically with no way to pin one meant a rollback first needed a Terraform change. The team also concluded that it needs better communication paths with application teams during incidents.

   View case
2. IL-0144 A systemd security update installed by unattended-upgrades lost the DNS configuration of Ubuntu 18.04 VMs, so AKS kubelets could not resolve registry names and pods failed with ImagePullBackOff

   Microsoft Azure2022

   Symptoms

   From 06:00 UTC on 30 August 2022, Azure VMs running Ubuntu 18.04 (bionic) with unattended-upgrades enabled began failing DNS resolution and losing network connectivity. Several Azure teams, among them the AKS and Azure Container Apps teams, were alerted by production alerts shortly after the update packages were published.

   DNS resolution failuresImage pull failuresMonitoring outage

   Trigger

   Unattended-upgrades on Ubuntu 18.04 VMs installed a Canonical security update published at 06:00 UTC on 30 August 2022, including systemd version 237-3ubuntu10.54.

   Root cause

   Breaking change in an upgrade

   Component

   Node operating system imagekubeletContainer registry and its credentialsClient-side DNS resolver and cache

   Contributing factor

   No staged rolloutExcessive blast radiusAutomation amplification

   Detection

   Several Azure teams, including AKS and Azure Container Apps, were alerted by production alerts shortly after the packages were published; incoming support cases then confirmed which Ubuntu versions were affected.

   Remediation

   • pointed customers to Canonical's description of the systemd bug and its fix
   • recommended rebooting affected VMs or running a template script that repairs DNS resolution
   • built automatic detection and remediation for AKS nodes and rolled it out across all regions
   • mitigated the remaining AKS customers manually through support

   Action items

   • Review the process that lets critical security updates bypass Safe Deployment Practices
   • Improve monitoring of the AKS data plane to alert on an uptick of errors
   • Review AKS monitoring algorithms so that similar VM errors are detected and alerted on
   • Establish an improved escalation path to Canonical during outages and add it to internal Technical Service Guides
   • AKS takes full control of the node security patch mechanism, with additional testing and controlled release of patches (estimated December 2022)
   • Work with Canonical to run dedicated tests on proposed packages before they are published for Azure IaaS VMs
   • Establish a process with Canonical to close the testing gap for the upgrade scenario (estimated March 2023)
   • Give AKS customers maintenance window control and environment staging for these patches (estimated December 2023)

   Lessons

   Security patches applied automatically by unattended-upgrades, once a day by default, and outside Azure's Safe Deployment Practices reached Ubuntu 18.04 VMs in every Azure region, so one systemd regression became a DNS outage across Azure. On AKS, lost node DNS showed up as image pull failures such as ImagePullBackoff, because kubelet could not resolve the registry. Azure plans to put node security patching under AKS's control with testing and controlled release; customers can use automatic node image upgrade for AKS, or automatic VM guest patching for VMs, instead of unattended-upgrades.

   View case

By root cause2