|
| 1 | +--- |
| 2 | +title: Troubleshoot Pod scheduler Errors in Azure Kubernetes Service |
| 3 | +description: Explains common scheduler errors, their causes, and how to resolve them. |
| 4 | +ms.date: 06/30/2025 |
| 5 | +ms.reviewer: |
| 6 | +ms.service: azure-kubernetes-service |
| 7 | +ms.custom: sap:Node/node pool availability and performance |
| 8 | +--- |
| 9 | + |
| 10 | +# Troubleshoot pod scheduler errors in Azure Kubernetes Service |
| 11 | + |
| 12 | +When you deploy workloads in Azure Kubernetes Service (AKS), you might encounter scheduler errors that prevent Pods from running. This article provides solutions to common scheduler errors. |
| 13 | + |
| 14 | +## Error: 0/(X) nodes are available: Y node(s) had volume node affinity conflict |
| 15 | + |
| 16 | +> [!NOTE] |
| 17 | +> X and Y represent the number of nodes. These values depend on your cluster configuration. |
| 18 | + |
| 19 | +Pods remain in the Pending state with the following scheduler error: |
| 20 | + |
| 21 | +>0/(X) nodes are available: Y node(s) had volume node affinity conflict. |
| 22 | +
|
| 23 | +### Cause |
| 24 | + |
| 25 | +[Persistent Volumes](https://kubernetes.io/docs/concepts/storage/persistent-volumes/#node-affinity) define `nodeAffinity` rules that restrict which nodes can access the volume. If none of the available nodes satisfy the volume's affinity rules, the scheduler cannot assign the Pod to any node. |
| 26 | + |
| 27 | +### Solution |
| 28 | + |
| 29 | +1. Review the node affinity set on your Persistent Volume resource: |
| 30 | + |
| 31 | + ```bash |
| 32 | + kubectl get pv <pv-name> -o yaml |
| 33 | + ``` |
| 34 | +2. Check node labels in the cluster: |
| 35 | + |
| 36 | + ```bash |
| 37 | + kubectl get nodes --show-labels |
| 38 | + ``` |
| 39 | +3. Make sure that at least one node's labels match the `nodeAffinity` specified in the Persistent Volume's YAML spec. |
| 40 | +4. To resolve the conflict, Update the Persistent Volume's `nodeAffinity` rules to match existing node labels or add the required labels to the correct node: |
| 41 | +
|
| 42 | + ```bash |
| 43 | + kubectl label nodes <node-name> <key>=<value> |
| 44 | + ``` |
| 45 | + Or, modify the PV's affinity rules to match existing node labels. |
| 46 | +5. After resolving the conflict, monitor the Pod status or retry the deployment. |
| 47 | + |
| 48 | + |
| 49 | +## Error: 0/(X) nodes are available: Insufficient CPU |
| 50 | + |
| 51 | +Pods remain in the Pending state with the scheduler error: |
| 52 | + |
| 53 | +>Error: 0/(X) nodes are available: Insufficient CPU. |
| 54 | + |
| 55 | +### Cause |
| 56 | + |
| 57 | +This issue occurs when one or more of the following conditions are met: |
| 58 | + |
| 59 | +- All node resources are in use. |
| 60 | +- The pending Pod's resource requests exceed available CPU on the nodes. |
| 61 | +- The node pools lack sufficient resources or have incorrect configuration settings. |
| 62 | +
|
| 63 | +### Solution |
| 64 | +
|
| 65 | +1. Review CPU usage on all nodes and verify if there is enough unallocated CPU to meet the pod's request. |
| 66 | + |
| 67 | + ```bash |
| 68 | + kubectl describe pod <pod-name> |
| 69 | + kubectl describe nodes |
| 70 | + ``` |
| 71 | +2. If no node has enough CPU, increase the number of nodes or use larger VM sizes in the node pool: |
| 72 | + |
| 73 | + ```bash |
| 74 | + |
| 75 | + az aks nodepool scale \ |
| 76 | + --resource-group <resource-group> \ |
| 77 | + --cluster-name <aks-name> \ |
| 78 | + --name <nodepool-name> \ |
| 79 | + --node-count <desired-node-count> |
| 80 | + ``` |
| 81 | +3. Optimize Pod resource requests. Make sure that CPU requests and limits are appropriate for your node sizes. |
| 82 | +4. Verify if any scheduling constraints are restricting pod placement across available nodes. |
| 83 | + |
| 84 | +## Error: 0/(X) nodes are available: Y node(s) had untolerated taint |
| 85 | + |
| 86 | +Pods remain in the Pending state with the error: |
| 87 | + |
| 88 | +>Error: 0/(X) nodes are available: Y node(s) had untolerated taint. |
| 89 | + |
| 90 | +### Cause |
| 91 | + |
| 92 | +The Kubernetes scheduler tries to assign the Pod to a node, but all nodes are rejected for one of the following reasons: |
| 93 | + |
| 94 | +- The node has a taint (`key=value:effect`) that the Pod doesn't tolerate. |
| 95 | +
|
| 96 | +- The node has other taint-based restrictions that prevent the Pod from being scheduled. |
| 97 | +
|
| 98 | +### Solution |
| 99 | +
|
| 100 | +1. Check node taints: |
| 101 | + ```bash |
| 102 | + kubectl get nodes -o json | jq '.items[].spec.taints' |
| 103 | + ``` |
| 104 | +2. Add necessary tolerations to Pod spec: Edit your deployment or Pod YAML to include matching tolerations for the taints on your nodes. For example, if your node has the taint key=value:NoSchedule, your Pod spec must include: |
| 105 | +
|
| 106 | + ```yml |
| 107 | + tolerations: |
| 108 | + - key: "key" |
| 109 | + operator: "Equal" |
| 110 | + value: "value" |
| 111 | + effect: "NoSchedule" |
| 112 | + ``` |
| 113 | + If the taint isn't needed, you can remove it from the node: |
| 114 | + |
| 115 | + ```bash |
| 116 | + kubectl taint nodes <node-name> <key>:<effect>- |
| 117 | + ``` |
| 118 | +4. Redeploy or monitor the Pod status: |
| 119 | + |
| 120 | + ```bash |
| 121 | + kubectl get pods -o wide |
| 122 | + ``` |
| 123 | +## Reference |
| 124 | + |
| 125 | +- [Kubernetes: Use Azure Disks with Azure Kubernetes Service](/azure/aks/azure-disks-dynamic-pv) |
| 126 | +- [Kubernetes: Use node taints](/azure/aks/use-node-taints) |
| 127 | +- [Kubernetes Documentation: Insufficient CPU](https://kubernetes.io/docs/concepts/scheduling-eviction/resource-bin-packing/#insufficient-resource) |
| 128 | +- [Kubernetes Documentation: Assign and Schedule Pods with Taints and Tolerations](https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/) |
| 129 | + |
| 130 | +[!INCLUDE [Third-party disclaimer](../../../includes/third-party-contact-disclaimer.md)] |
| 131 | +[!INCLUDE [Azure Help Support](../../../includes/azure-help-support.md)] |
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