Cases32 cases

25 to 29 of 32

1. IL-0469 The managed Azure Kubernetes API server for the data100 hub stopped answering, so the stopped hub pod was not recreated

   UC Berkeley2019

   Symptoms

   On 25 February 2019 the Kubernetes API server of the managed Azure cluster running the data100 hub became unreachable. kubectl failed for every operation and requests to create new resources failed, so when the hub pod stopped, no new one was created and users saw a proxy error message.

   Control plane unresponsiveService outage

   Root cause

   Cloud provider outage

   Component

   AKS control planeKubernetes API serverkubelet

   Contributing factor

   Limited debug access

   Detection

   Infrastructure staff were notified in Slack at 11:34 and found that kubectl failed for all operations while the hub proxy was up.

   Remediation

   • Created a new cluster and requested a new NFS server in its resource group
   • Detached the data volumes from the old NFS server and moved them to the new cluster's resource group
   • Imported the ZFS pool into the new NFS server
   • Created the staging hub with helm and updated DNS
   • Created the prod hub with helm and updated DNS

   Action items

   • Monitor the API server endpoint remotely and alert when it is down

   View case
2. IL-0505 kubectl logs failed on GKE with "No SSH tunnels currently open" and mybinder.org build logs stopped reaching users

   Binder Project2019

   Symptoms

   On 20 February 2019 at 08:03 CET, `kubectl logs -f <pod>` stopped working for every pod in the mybinder.org cluster on GKE. Because pod logs could not be read, build logs were no longer forwarded to users, although the builds themselves ran normally.

   Monitoring outageDeploys failing

   Root cause

   Cloud provider outage

   Component

   GKE control planeKubernetes API server

   Contributing factor

   Limited debug access

   Remediation

   • Cordoned node gke-prod-a-users-b921bb88-rd5d so it would be removed from the pool once empty
   • Drained the node and removed it from the pool, after which kubectl logs worked again

   Action items

   • Test that kubectl logs works and notify when it does not
   • Add the command for retrieving API server logs to the SRE guide
   • Describe in the SRE guide how to identify suspicious node networking status

   Lessons

   The root cause was very difficult to identify, partly because it appears to sit in the Kubernetes master or the GKE service itself. Capturing `kubectl describe node` for the suspicious node would have allowed a comparison with healthy nodes, and a node that reports no ExternalIP or InternalIP in its status was likely a direct symptom of the problem and can be used as a diagnostic in the future.

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3. IL-0030 Most nodes of a cluster went NotReady together for 15 minutes while the API server sat behind an AWS ELB

   Zalando2019

   Symptoms

   Fewer than 20% of the nodes in one Zalando cluster were available. Most nodes reported NotReady at the same moment, and only a handful stayed Ready.

   Node NotReady

   Root cause

   Software defect

   Component

   Kubernetes API serverCloud load balancer

   Contributing factor

   Unpatched known bug

   Remediation

   • none; the nodes recovered on their own after about 15 minutes

   View case
4. 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.

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5. IL-0031 Kubernetes API server OOM-killed, leaving the Skipper ingress without routes; the talk points to a misconfigured CronJob manifest

   Zalando2018

   Symptoms

   Customers were affected, and Zalando's IAM service answered requests with HTTP 404. The talk shows this on slides titled "Customer impact" and "IAM returning 404", followed by a slide on the number of pods in the cluster.

   High error rateControl plane unresponsiveOOMKilled

   Trigger

   A CronJob (apiVersion batch/v2alpha1, schedule "*/15 9-19 * * Mon-Fri") whose concurrencyPolicy: Forbid and job history limits sat inside the pod template spec instead of the CronJob spec. The talk shows it right after the slides on the number of pods and the API server being OOM-killed, and the lessons add a quota on the number of pods.

   Root cause

   Capacity exhaustion

   Component

   Kubernetes API serverIngress controller

   Contributing factor

   Single point of failureExcessive blast radius

   Remediation

   • fixed the CronJob manifest: moved concurrencyPolicy: Forbid and the job history limits to the CronJob spec, added activeDeadlineSeconds: 120 and changed the schedule to "7 8-18 * * Mon-Fri"

   Action items

   • Make the ingress stay healthy during API server problems
   • Make the ingress keep the last known set of routes
   • Use a ResourceQuota on the number of pods (the example sets pods: "1500")

   Lessons

   An AWS ALB routes traffic to all hosts when all hosts report unhealthy, so the ingress should stay healthy during API server problems. An ingress controller that reads routes from the API server should keep its last known set of routes. Use a quota for the number of pods.

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