Pod Scheduling Failure Diagnosis

When a pod is stuck in Pending state, follow this flow to identify why the scheduler cannot place it on a node.

Scope: This skill is for diagnosis only. Once you identify the root cause, report it to the user and stop. Do NOT attempt to modify node taints, labels, or pod specs — that should be left to the user.

Diagnostic Flow

1. Describe the pod

kubectl describe pod <pod> -n <ns>

Focus on the Events section. The scheduler's FailedScheduling event contains the reason. Note the full event message — it lists how many nodes were evaluated and why each was rejected.

2. Match scheduling failure and investigate

Match the FailedScheduling message against the patterns below.

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Insufficient cpu / Insufficient memory — Not enough resources

No node has enough allocatable CPU or memory to satisfy the pod's resource requests.

Check node resource usage:

kubectl top nodes

Check what the pod is requesting:

kubectl get pod <pod> -n <ns> -o jsonpath='{.spec.containers[*].resources.requests}'

Advise the user to either reduce the pod's resource requests, scale up existing nodes, or add new nodes to the cluster.

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didn't match Pod's node affinity/selector — Node affinity/selector mismatch

The pod has a nodeSelector or nodeAffinity that no available node satisfies.

Check the pod's node selection criteria:

kubectl get pod <pod> -n <ns> -o jsonpath='{.spec.nodeSelector}'
kubectl get pod <pod> -n <ns> -o jsonpath='{.spec.affinity}'

Check available node labels:

kubectl get nodes --show-labels

Advise the user to either update the pod's selector/affinity or add the required labels to appropriate nodes.

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had taint ... that the pod didn't tolerate — Taint/toleration mismatch

Nodes have taints that the pod does not tolerate.

Check node taints:

kubectl get nodes -o custom-columns='NAME:.metadata.name,TAINTS:.spec.taints[*].key'

Check the pod's tolerations:

kubectl get pod <pod> -n <ns> -o jsonpath='{.spec.tolerations}'

Advise the user to either add the appropriate toleration to the pod or remove the taint from a node.

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persistentvolumeclaim ... not found / not bound — PVC issue

The pod references a PVC that does not exist or is not bound to a PV.

Check PVC status:

kubectl get pvc -n <ns>

If the PVC exists but is Pending, check its events:

kubectl describe pvc <pvc-name> -n <ns>

Common causes: no matching PV, StorageClass not found, or provisioner failed.

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0/N nodes are available (all filtered) — No nodes available

Every node in the cluster was rejected. The message usually lists multiple reasons. Address each reason individually — the most impactful one is typically resource insufficiency or taints.

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didn't find available persistent volumes — No matching PV

The PVC exists but no PV matches its requirements (size, access mode, storage class).

kubectl get pv
kubectl get pvc <pvc-name> -n <ns> -o yaml

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pod has unbound immediate PersistentVolumeClaims — PVC not yet bound

The PVC is waiting for a PV to be provisioned. Check if the StorageClass provisioner is working:

kubectl get storageclass
kubectl get events -n <ns> --field-selector involvedObject.name=<pvc-name>

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Preempting — Scheduler is preempting lower-priority pods

The scheduler is attempting to evict lower-priority pods to make room. This is normal behavior for priority-based scheduling. If the pod remains Pending after preemption, there may be additional constraints.

Notes

• If no FailedScheduling event exists, the pod may not have been processed by the scheduler yet — check if the scheduler pod itself is healthy: kubectl get pods -n kube-system -l component=kube-scheduler.
• For pods created by controllers (Deployment, StatefulSet), the pending pod name may change as the controller recreates it — use label selectors to find the current pending pod.