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1. IL-0459 MediaWiki on Kubernetes terminated TLS with a wrong certificate after a deployment, and 1% of requests failed

   Wikimedia Foundation2023

   Symptoms

   On 9 August 2023, right after a MediaWiki configuration deployment at 11:41 UTC, the MediaWiki deployments on Kubernetes terminated TLS with a wrong certificate, and about 1% of Wikimedia web and API traffic, around 120 requests per second, received errors for about 30 minutes. The issue was detected by a page for failed service probes on mw-api-ext and mw-api-int.

   High error rateTLS certificate errorsControl plane lag

   Trigger

   At 09:37 a change to the global Kubernetes defaults was merged that switched supported charts to cert-manager certificates. The next MediaWiki on Kubernetes deployment, a configuration change at 11:41, picked it up.

   Root cause

   Configuration change

   Component

   cert-managerHelm

   Contributing factor

   Change with a delayed effectNo configuration tests

   Detection

   A page from the ProbeDown alerts for mw-api-ext:4447 and mw-api-int:4446 at 11:47; a KubernetesAPILatency alert had fired at 11:46.

   Remediation

   • Identified the issue and prepared a patch, https://gerrit.wikimedia.org/r/947331
   • Redeployed the MediaWiki deployments on Kubernetes

   Action items

   • Review whether deployment procedures and testing should be strengthened, for example against surprising changes on the next deployment and with canary deployments for Kubernetes
   • Look at metrics that become unavailable or unhealthy during deployments, or at reducing the impact of deployments

   Lessons

   The cause was found quickly because the person who made the breaking change was responding. The change should have been caught by CI, but the repository it was made in (hieradata) does not run the CI of the deployment charts. Only 1% of traffic going to Kubernetes kept the impact small, and the low error volume made it slower to link the errors to Kubernetes.

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2. 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.

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