Cases2 cases

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1. IL-0230 kube-proxy sync failures during a Kubernetes upgrade corrupted node iptables, and CircleCI jobs stopped starting

   CircleCI2023

   Symptoms

   On 14 March 2023 at about 18:00 UTC, communication errors rose on one CircleCI service, and pipelines for all customers began to start late until jobs did not run at all. Within an hour the errors had spread to many services and to every function of the application, including the CircleCI UI and API.

   Service outageIntermittent connection failuresDNS resolution failures

   Trigger

   At about 17:40 UTC on 14 March the infrastructure team resumed the upgrade of the main production Kubernetes cluster with a changed approach for some components, after a first attempt on 13 March had been rolled back. The ongoing upgrade left kubelet and kube-proxy at mismatched versions.

   Root cause

   Breaking change in an upgrade

   Component

   kube-proxykubeletCoreDNSClient-side DNS resolver and cache

   Contributing factor

   Partial rolloutIneffective rollbackMonitoring blind spotHarmful manual action

   Detection

   At 18:00 UTC engineers saw communication errors rise on one service, then job processing delays climbing and job queues backing up across several services. The kube-proxy "Sync failed" errors were found only in the analysis after the incident.

   Remediation

   • Restarted every node in the cluster so each node built a fresh iptables ruleset
   • Restarted a separate pool of dependencies so jobs using contexts or the machine executor ran again
   • Added capacity to work through the backlog of jobs
   • Restarted the RabbitMQ nodes to fix a few corrupted queues

   Action items

   • Improve the Kubernetes upgrade process to limit the risk of future upgrades
   • Add metrics and alerts for kube-proxy sync errors
   • Evaluate ways to make the RabbitMQ infrastructure more resilient

   Lessons

   No single trigger caused the incident. Because networking underlies everything in the cluster, Kubernetes upgrades carry inherent risk, and CircleCI's risk mitigation did not hold up when several events interacted.

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2. IL-0086 A deployment meant for a CircleCI test Kubernetes cluster also removed Traefik and Calico resources from the production cluster, taking down the CircleCI UI and runner.circleci.com

   CircleCI2021

   Symptoms

   At 15:35 EST on 11 March 2021 the CircleCI web UI and runner.circleci.com became unavailable. The API, which uses a separate ingress point, stayed reachable, and builds kept running.

   Service outageResources deleted

   Trigger

   An update deployed to a test Kubernetes cluster also removed Traefik and Calico resources from CircleCI's primary production cluster.

   Root cause

   Faulty deployment

   Component

   Ingress controllerCalico

   Contributing factor

   Excessive blast radiusNo runbookMonitoring blind spot

   Detection

   CircleCI engineers were alerted and began investigating. The status page posted its first notice at 20:45 UTC.

   Remediation

   • restored Traefik in the production cluster
   • restored Calico in the production cluster, after which pods served customer requests again

   Action items

   • Improve network-level documentation and runbooks to cover every layer of the Kubernetes networks
   • Improve monitoring and alerting for the network infrastructure
   • Add guardrails that isolate the production and staging clusters so they cannot interfere with each other

   Lessons

   A deployment path that can reach both a test cluster and production can remove shared networking components from production. When the ingress controller and the CNI are both affected, restoring the ingress alone is not enough: engineers had to find the link between Calico and Traefik and restore Calico before pods served traffic again. Time went to DNS and AWS red herrings because nothing linked the outage to the test deployment; CircleCI's answer is better network runbooks, network alerting and guardrails between clusters.

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