Incident Library
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Cases3 cases

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  1. IL-0060 Kubernetes 1.24 upgrade removed the master node label that Calico route reflectors selected on, dropping all pod routes and taking Reddit down for 314 minutes
    Reddit2023
    Symptoms

    About two minutes after an engineer started the Kubernetes 1.23 to 1.24 upgrade of the cluster running Reddit's legacy stack, just after 19:00 UTC, the site stopped. The CDN edge request graph, which is kept separate from the cluster, showed traffic by status collapsing. Users saw the error page, a homepage with no posts, or plain errors.

    Service outageHigh error rateDNS resolution failuresMonitoring outagePods stuck in ContainerCreatingControl plane lag
    Trigger

    An in-place upgrade of the legacy cluster from Kubernetes 1.23 to 1.24; in 1.24 the node-role.kubernetes.io/master label is removed even from running clusters.

    Root cause
    Breaking change in an upgrade
    Component
    CalicoKubernetes API serverAdmission webhooketcd
    Contributing factor
    Configuration not in codeUnrepresentative stagingUntested backupMonitoring blind spotSingle point of failure
    Detection

    The site broke about two minutes into the upgrade; an incident was opened immediately and responders were on the call within three minutes, working from CDN edge graphs because the cluster's own metrics were gone.

    Remediation
    • deleted the Open Policy Agent webhook configurations to stop API server timeouts
    • terminated all worker nodes of the cluster
    • restored the control plane from the pre-upgrade backup onto the first control plane node
    • switched off the cluster autoscaler until the control plane was stable
    • generated new TLS certificates so replacement control plane nodes could join etcd
    • brought traffic back in steps from 1% to 100%
    • restarted legacy services that had been stopped by hand
    Action items
    • Codify cluster configuration so every choice has a record, and document in detail what cannot be codified
    • Standardise components across clusters and replace bespoke configurations
    • Build tooling to manage the lifecycle of whole clusters so they can be recreated or replicated
    • Add pre-production clusters that can be tested with confidence
    • Improve the backup restore process and make cluster upgrades safe
    Lessons

    Configuration that exists only in a live cluster, edited by hand through a special tool, can be forgotten, as the route reflector setup was, and then break on an upgrade nobody connects it to. A Kubernetes upgrade cannot be reverted without a restore, so the restore procedure has to be kept current and practised. Consistent, codified clusters are what make upgrades testable; bespoke clusters keep producing outages.

    View case
  2. 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
  3. IL-0075 Kubernetes API servers pegged on CPU when the cluster grew to about 290 nodes, traced to Datadog agents polling the API
    Civis Analytics2019
    Symptoms

    After Civis released its new script infrastructure on Kubernetes internally in September 2018, developers reported that kubectl commands were slow, and users intermittently could not start notebooks and services.

    Control plane lagControl plane unresponsiveHigh latencyHigh error rateDNS resolution failures
    Trigger

    Migrating clients' Python, R and container scripts from the in-house Bocce system to Kubernetes (the project called Croquet) pushed the cluster to about 290 EC2 instances under a large script load.

    Root cause
    Capacity exhaustion
    Component
    Kubernetes API serverTelemetry agentetcd
    Contributing factor
    Unknown limitUnverified assumptionMonitoring blind spotNo capacity planning
    Detection

    Developer reports of slow kubectl commands and user reports of notebooks and services failing to start, then high CPU on the master nodes.

    Remediation
    • moved internal users back to the old Bocce infrastructure
    • resized the three master nodes from m4.large to m4.4xlarge
    • changed the Datadog setup so per-node agents no longer polled the API server for service metadata
    • raised max-requests-inflight for non-mutating requests from 400 to 1200
    • grew the etcd EBS volumes from 20 to 100 GB (100 to 300 IOPS)
    • switched client scripts from the ClusterFirst DNS policy to Default
    Action items
    • Upgrade etcd from 2.2.1 to 3.x once Kops supports a safe migration
    • Solve the in-cluster DNS timeouts so client scripts can talk to other workloads in the cluster
    Lessons

    Kubernetes can reach thousands of nodes only after tuning, and third-party DaemonSets are a common cause of control plane load: an agent on every node that polls or watches the API server multiplies with the cluster size. Datadog, kube2iam and the fluentd metadata filter all showed this. A small configuration change often fixes it, but finding it took load testing and the API server access logs.

    View case
Check your cluster for this

These 3 cases involve Kubernetes API server and Admission webhook. kubegap audits a Kubernetes cluster for gaps like these, read-only, from Claude Code or Codex; its checks cite public reports like the ones in this library.

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By root cause3

Breaking change in an upgrade1 case

Component
Admission webhookCalicoetcdKubernetes API server
Contributing factor
Untested backupConfiguration not in codeMonitoring blind spotSingle point of failureUnrepresentative staging
Organisation
Reddit
  1. IL-0060 Kubernetes 1.24 upgrade removed the master node label that Calico route reflectors selected on, dropping all pod routes and taking Reddit down for 314 minutes
    Reddit2023

Configuration change1 case

Component
Admission webhookKubernetes API server
Contributing factor
Unverified assumptionMonitoring blind spotNo configuration tests
Organisation
DFDS
  1. IL-0108 An Alcide admission controller applied to the production cluster during a workshop made create and update requests on Deployments time out
    DFDS2020

Capacity exhaustion1 case

Component
etcdKubernetes API serverTelemetry agent
Contributing factor
Unverified assumptionUnknown limitMonitoring blind spotNo capacity planning
Organisation
Civis Analytics
  1. IL-0075 Kubernetes API servers pegged on CPU when the cluster grew to about 290 nodes, traced to Datadog agents polling the API
    Civis Analytics2019