Cases11 cases

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1. IL-0090 After an upgrade of the ModSec ingress controller module, its validating webhook served a certificate for the wrong service name and blocked every Ingress create and change

   UK Ministry of Justice2021

   Symptoms

   At 13:15 on 9 June 2021 a user reported in the #ask-cloud-platform channel that deploying a UAT application failed on its Ingress resource.

   Deploys failing

   Trigger

   The Cloud Platform team upgraded the ModSec ingress controller module to v3.33.0; the deployment appeared to succeed.

   Root cause

   Breaking change in an upgrade

   Component

   Admission webhookIngress controller

   Contributing factor

   Unrepresentative staging

   Detection

   A user reported the deployment error in the #ask-cloud-platform Slack channel at 13:15.

   Remediation

   • rolled back the ModSec ingress controller module to v0.0.7

   Action items

   • Find out why the issue was not flagged in the test cluster and try to reproduce it, possibly with a new test (ticket #2972)
   • Add a smoke test that checks the alerts in Alertmanager (ticket #2973)
   • Add a helloworld app that uses the ModSec controller so smoke tests can check that traffic works (ticket #2974)
   • Make a new version of the ModSec module work on EKS for both live-1 and live; neither the old nor the new version works on live (ticket #2975)

   View case
2. IL-0032 Mutating admission controller generated broken JSON patches, silently blocking deploys for a week until a production service ran down to two pods

   Airbnb2020

   Symptoms

   A production service at Airbnb showed a high error rate and could not be deployed. The deploy failed with a cryptic Kubernetes error about being unable to access invalid index 5.

   High error rateThroughput degradationDeploys failing

   Trigger

   A change to the mutating admission controller, which had been rolled out within the previous month, had gone in seven days before the incident surfaced; when it had to delete two items from an array in a spec, it generated an invalid JSON patch that removed index 2 and then index 3.

   Root cause

   Software defect

   Component

   Admission webhookHorizontal pod autoscaler

   Contributing factor

   Change with a delayed effectMonitoring blind spotIgnored early signal

   Detection

   The affected service reported a high error rate and its deploy failed; the slow degradation of other services over the previous seven days had gone unnoticed.

   Remediation

   • deleted the mutating admission controller from the affected cluster

   Action items

   • Create alerts from the existing metrics that would have shown the problem earlier

   Lessons

   Keep in mind that a mutating admission controller exists in the cluster; a recently added one is easy to forget during an incident. Search for the exact error message early instead of working on the visible symptoms. Page a teammate when progress stalls.

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3. IL-0108 An Alcide admission controller applied to the production cluster during a workshop made create and update requests on Deployments time out

   DFDS2020

   Symptoms

   At 14:41 CET on 4 November 2020 users reported timeouts when deploying to Hellman, the production Kubernetes cluster. The timeouts were confirmed at 15:04.

   Deploys failingControl plane lag

   Trigger

   During an Alcide workshop that began at 13:00 CET, an Alcide admission controller was applied to the production cluster at 13:13 in the belief that it would not disrupt anything.

   Root cause

   Configuration change

   Component

   Admission webhookKubernetes API server

   Contributing factor

   No configuration testsUnverified assumptionMonitoring blind spot

   Detection

   Users reported timeouts when deploying to the Hellman cluster at 14:41 CET; the timeouts were verified at 15:04.

   Remediation

   • toggled the Alcide admission controller to verify that it caused the timeouts
   • permanently deleted the Alcide admission controller

   Action items

   • Monitor Kubernetes deployments for timeouts
   • Monitor 5xx status codes from the Kubernetes API server

   Lessons

   New components are applied in sandbox clusters, not in production. The team needs enough Alcide knowledge to maintain the component until it is fully deprecated.

   View case
4. IL-0088 A validating admission webhook added by a new ingress controller module version made the live-1 cluster reject every new Ingress with an x509 error

   UK Ministry of Justice2020

   Symptoms

   At 12:39 on 7 September 2020 the Cloud Platform team found that the Ingress API of the live-1 cluster was refusing every POST request. A user who provisioned a new service could not create an ingress into the cluster. The incident was declared at 12:54.

   Deploys failing

   Trigger

   Version 0.1.0 of the team's ingress controller module started creating a ValidatingWebhookConfiguration resource, and one new 0.1.0 ingress controller in the live-1 cluster failed to be created because of AWS resource limits.

   Root cause

   Faulty deployment

   Component

   Admission webhookIngress controller

   Contributing factor

   Single point of failure

   Detection

   The Ingress API was found refusing 100% of POST requests at 12:39; the incident was declared at 12:54.

   Remediation

   • removed by hand all the additional admission controllers created by module version 0.1.0
   • removed the admission webhook from the ingress controller module and released version 0.1.1
   • upgraded every ingress module on version 0.1.0 to 0.1.1

   Lessons

   Turning on the validating webhook in the shared ingress controller module made the webhook a single point of failure for every ingress controller pod in the ingress-controllers namespace: when one controller could not come up, no team could create an ingress.

   View case
5. IL-0008 An unresponsive OPA validating webhook crash-looped the API server during a GKE master upgrade, and node auto-repair then recreated every node

   Jetstack2019

   Symptoms

   Jetstack was upgrading the master of a development cluster that many teams use to test their apps during the working day, a regional Google Kubernetes Engine (GKE) cluster in europe-west1. The upgrade ran through Jetstack's GKE Terraform pipeline and did not finish before the 20-minute Terraform timeout, while the GKE console still showed the cluster as upgrading.

   Upgrade stallControl plane unresponsiveNode recreation loopService outage

   Trigger

   A planned master upgrade of the shared development cluster. The same upgrade had been done on another pre-production environment earlier that day, and no API downtime was expected.

   Root cause

   Configuration change

   Component

   Admission webhookGKE control planeKubernetes API serverkubelet

   Contributing factor

   Excessive blast radiusNo health probesMonitoring blind spotAutomation amplification

   Detection

   The first sign was the master upgrade missing the 20-minute Terraform timeout; re-running the pipeline returned the kube-apiserver unhealthy error. The cause was identified with the help of Google Support.

   Remediation

   • Deleted the OPA ValidatingAdmissionWebhook resource during a window of API server access

   Action items

   • Limit the OPA webhook to the namespaces where the policy applies and development teams have access
   • Enable the webhook only for Ingress and Service resources, the only resources the policy validates
   • Add a liveness probe so OPA is restarted when it stops responding, and update the OPA documentation
   • Follow the open upstream Kubernetes issue about this behaviour

   Lessons

   With alerting on API server response times, the team might have seen CREATE and UPDATE requests slow down across the board as soon as the OPA-backed webhook was first deployed. Every workload needs probes: OPA looked so simple to deploy that the team skipped the Helm chart, which adds a livenessProbe for the admission controller containers among other adjustments to the tutorial configuration. Others had hit the same problem, and an upstream issue to improve it was still open.

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