Incident Library
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Cases2 cases

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  1. IL-0208 A GitLab chart bump that renamed Kubernetes Service and Deployment ports made the GCP load balancer reconfigure, and GitLab.com slowed down and returned intermittent 50x errors
    GitLab2022
    Symptoms

    At 07:53 UTC on 2022-03-31 the rate of 50x errors on GitLab.com went up, and at 07:54 PagerDuty paged the engineer on call (EOC) about the rising error rate. Users saw slow pages and intermittent 50x error pages. The incident lists the Web, API, Git and Pages services as affected.

    High error rateHigh latencyIntermittent timeouts
    Trigger

    A k8s-workloads/gitlab-com pipeline deployed merge request !1643, a GitLab chart bump that changed the port names of Kubernetes Services and Deployments (related to the Prometheus service and pod monitors), starting with the canary environment gprd-cny at 07:49 UTC.

    Root cause
    Configuration change
    Component
    HelmCloud load balancerHAProxy
    Contributing factor
    Automation amplification
    Detection

    A PagerDuty alert on the rising error rate paged the EOC at 07:54 UTC, one minute after the 50x errors went up. The engineer deploying the change noticed the errors and linked them to it.

    Remediation
    • drained the canary environment and re-enabled it after twenty minutes
    • cancelled the deployment jobs for clusters c and d before they started
    • drained gprd-us-east1-d in HAProxy and re-enabled it five minutes later
    • raised the minimum replica count above 100 (merge request !1650)
    • drained gprd-us-east1-c in HAProxy, deployed the change to it, and re-enabled it
    • reverted the minimum replica increase (merge request !1652)
    Action items
    • Implement graceful draining of a whole regional cluster
    • Create a Chatops command that puts PagerDuty into maintenance mode
    Lessons

    Renaming ports on Kubernetes Services and Deployments behind a GCP load balancer made the load balancer reconfigure, and requests were slow or timed out until the new configuration had fully applied, which took minutes. GitLab notes that alerting worked well. The follow-up work is a way to drain a whole regional cluster gracefully and a Chatops command to put PagerDuty into maintenance mode.

    View case
  2. IL-0209 A too-high HPA CPU target kept GitLab.com web pods from scaling up as traffic moved from VMs to Kubernetes, breaching the web latency SLO for 15 minutes
    GitLab2021
    Symptoms

    The web service breached its latency SLO at 07:30 UTC and its Apdex dropped: some requests to the GitLab.com web front end slowed down for about 15 minutes. This happened while web traffic was being shifted from virtual machines to the web pods on Kubernetes, and the pods did not scale up as the traffic arrived.

    High latencyAutoscaler misbehaviour
    Trigger

    Shifting web traffic from VMs to Kubernetes pods during the GitLab.com web migration.

    Root cause
    Configuration change
    Component
    Horizontal pod autoscaler
    Contributing factor
    Unverified assumption
    Detection

    The web latency SLO breach at 07:30 UTC; an engineer declared the incident in Slack at 07:40.

    Remediation
    • Lowered the target CPU utilisation of the web pods' autoscaler to a more conservative value (merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1149)
    Action items
    • Adjust the target utilisation for the web pods (gitlab-com/gl-infra/k8s-workloads/gitlab-com!1149)
    Lessons

    When traffic is moved onto pods that rely on CPU-based autoscaling, a CPU target set too high can keep the pods from scaling as the traffic arrives; GitLab fixed it by setting a more conservative target.

    View case
Check your cluster for this

These 2 cases involve Cloud load balancer and HAProxy. 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 cause1

Configuration change2 cases

Component
Cloud load balancer1HAProxy1Helm1Horizontal pod autoscaler1
Contributing factor
Unverified assumption1Automation amplification1
Organisation
GitLab2
  1. IL-0208 A GitLab chart bump that renamed Kubernetes Service and Deployment ports made the GCP load balancer reconfigure, and GitLab.com slowed down and returned intermittent 50x errors
    GitLab2022
  2. IL-0209 A too-high HPA CPU target kept GitLab.com web pods from scaling up as traffic moved from VMs to Kubernetes, breaching the web latency SLO for 15 minutes
    GitLab2021