CKA
955 incident response problems that help with CKA prep.
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When the ConfigMap changed but the Pod keeps using the old valuesAn InfraTree guide that lays out the first signals to check, the CLI verification order, common misdiagnoses, and a safe recovery path when values don't refresh after a ConfigMap update because of envFrom, subPath, volume projection, or rollout trigger differences.Kubernetes3 min readWhen CoreDNS is Running but only DNS lookups failAn InfraTree guide that lays out the first signals to check, the CLI verification order, common misdiagnoses, and a safe recovery path when the CoreDNS Pod looks healthy but failures occur in the kube-dns path, upstream, node-local-dns, or policy.Kubernetes3 min readWhat to check first when CrashLoopBackOff appearsAn InfraTree guide that lays out the first signals to check, the CLI verification order, common misdiagnoses, and a safe recovery path when a Pod restarts repeatedly and the real cause is left in the previous logs and events.Kubernetes3 min read
Recommended problems
Reviewed problems first, then problems with detailed scenarios.
CICD-064Helm post-upgrade hook Job never completes and blocks the release promotion gateThe chart renders correctly, but the deployment never settles because a hook job keeps restarting and Helm treats the upgrade as unfinished.ReviewedCI/CDIntermediate20 minFreeCICD-103Helm post-renderer strips readiness probes from the canary manifest and Argo CD approves a broken rolloutThe application renders cleanly, but the post-processing step removes health checks from just the canary variant so progressive delivery never sees a meaningful gate.ReviewedCI/CDIntermediate18 minFreeK8S-001Organizing the first checkpoints for a CrashLoopBackOff PodLearn in what order to check logs, events, and config when looking at a Pod stuck in a restart loop.ReviewedKubernetesBeginner18 minFreeK8S-004ImagePullBackOff caused by a missing private registry credentialA situation where the image address is correct but a missing pull secret causes failure in only certain namespaces.ReviewedKubernetesBeginner17 minFreeK8S-008New workloads not schedulingA scenario that narrows down the root cause, centered on comparing the schedule conditions with the actual node labels, in the situation of new workloads not scheduling because node affinity is too strong.ReviewedKubernetesIntermediate21 minFreeK8S-011A readiness probe path typo keeps the rolling update from finishingA readiness probe path typo keeps the rolling update from finishing is a hands-on troubleshooting drill. A situation where the application is fine but only the probe path is wrong, so new Pods never become ready. Kubernetes Config and Rollouts needs to be checked by narrowing...ReviewedKubernetesBeginner16 minFree
All problems (955)
CrashLoopBackOff: pods keep restarting after a new releaseCrashLoopBackOff: pods keep restarting (CrashLoop and Restarts) is a hands-on troubleshooting drill. Read the previous container's log to find why a pod keeps restarting. kubernetes-workload-reliability needs to be checked by narrowing scope, recent change, and the current liv...ReviewedKubernetesBeginner3 minFreeImagePullBackOff: new pods cannot pull the release imageImagePullBackOff: new pods cannot pull the release image is a hands-on troubleshooting drill. Read the pull event to see what the registry could not find. container-startup needs to be checked by narrowing scope, recent change, and the current live signal before rollback. 실무에서...ReviewedKubernetesBeginner3 minFreeExit code 137 (OOMKilled): a container restarts under loadExit code 137 (OOMKilled): a container restarts is a hands-on troubleshooting drill. Learn what OOMKilled and exit code 137 mean. kubernetes-workload-reliability needs to be checked by narrowing scope, recent change, and the current live signal before rollback. 실무에서는 CrashLoop...ReviewedKubernetesBeginner3 minFreePending: new pods do not start after scaling outPending: new pods do not start (Resource Exhaustion) is a hands-on troubleshooting drill. Read a FailedScheduling event to see why a pod cannot be placed. Kubernetes Scheduling and Capacity needs to be checked by narrowing scope, recent change, and the current live signal befo...ReviewedKubernetesBeginner3 minFreeService calls fail: the endpoints list is emptyService calls fail: the endpoints list is empty is a hands-on troubleshooting drill. When a Service has no endpoints, compare its selector with the pod labels. cluster-networking-and-service-discovery needs to be checked by narrowing scope, recent change, and the current live...ReviewedKubernetesBeginner3 minFreeIngress 404 Not Found: only the newly added www host returns 404Ingress 404 Not Found: only the newly added www host returns 404 is a hands-on troubleshooting drill. Check that the request's host name matches an Ingress rule. NGINX Kubernetes Ingress and Traffic needs to be checked by narrowing scope, recent change, and the current live si...ReviewedKubernetesBeginner3 minFreeCICD-103Helm post-renderer strips readiness probes from the canary manifest and Argo CD approves a broken rolloutThe application renders cleanly, but the post-processing step removes health checks from just the canary variant so progressive delivery never sees a meaningful gate.ReviewedCI/CDIntermediate18 minFreeK8S-030Ingress class mismatch sends traffic to the wrong controllerIngress class mismatch sends traffic to the wrong controller is a hands-on troubleshooting drill. Routing rules are valid, but the ingress object is reconciled by a different controller than the team expected. Kubernetes Ingress and Traffic needs to be checked by narrowing sco...ReviewedKubernetesIntermediate19 minFreeCICD-064Helm post-upgrade hook Job never completes and blocks the release promotion gateThe chart renders correctly, but the deployment never settles because a hook job keeps restarting and Helm treats the upgrade as unfinished.ReviewedCI/CDIntermediate20 minFreeK8S-1192Core application restarts endlesslyA public probe example was copied into production. It worked in steady state, but after a cold deploy the app now gets killed before it can finish bootstrap.ReviewedKubernetesAdvanced21 minFreeK8S-011A readiness probe path typo keeps the rolling update from finishingA readiness probe path typo keeps the rolling update from finishing is a hands-on troubleshooting drill. A situation where the application is fine but only the probe path is wrong, so new Pods never become ready. Kubernetes Config and Rollouts needs to be checked by narrowing...ReviewedKubernetesBeginner16 minFreeK8S-034NetworkPolicy allows the app service but blocks CoreDNS resolutionThe namespace appears to have the right egress rules for the application path, yet pods still fail because DNS traffic to kube-dns was never permitted.ReviewedKubernetesIntermediate18 minFreeK8S-008New workloads not schedulingA scenario that narrows down the root cause, centered on comparing the schedule conditions with the actual node labels, in the situation of new workloads not scheduling because node affinity is too strong.ReviewedKubernetesIntermediate21 minFreeK8S-033PVC expansion succeeds in the API but filesystem size never changesStorageClass and claim expansion are enabled, yet the workload still hits a full disk because the filesystem inside the volume was never resized or remounted correctly.ReviewedKubernetesIntermediate22 minFreeK8S-036HPA stays idleMetrics look available and the pod is busy, but autoscaling does nothing because the target resource request needed for utilization math is missing.ReviewedKubernetesBeginner16 minFreeK8S-004ImagePullBackOff caused by a missing private registry credentialA situation where the image address is correct but a missing pull secret causes failure in only certain namespaces.ReviewedKubernetesBeginner17 minFreeK8S-001Organizing the first checkpoints for a CrashLoopBackOff PodLearn in what order to check logs, events, and config when looking at a Pod stuck in a restart loop.ReviewedKubernetesBeginner18 minFreeK8S-1612A CoreDNS pod is healthy and one namespace still resolves old namesOne namespace still resolves old names after a DNS suffix update.ReviewedKubernetesBeginner6 minFreeK8S-1611A pod is Running and one Service still has no endpointsA Service shows zero endpoints right after an app label rename.ReviewedKubernetesBeginner6 minFreeK8S-1631A Service is correct and one app still has no endpointsA Service still shows no endpoints after a label cleanup.ReviewedKubernetesBeginner6 minFree