Kubernetes - pod has unbound immediate PersistentVolumeClaims

Question

I\'m using mysql Kubernetes statefulset, i mapped PVs to host directory (CentOS 8 VM) but getting \" pod has unbound immediate PersistentVolumeClaims\"

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Answer 1

The mentioned error can be caused for multiple reasons - below are few options which I encountered.

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Example 1

The persistentvolume-controller has failed to find a PV with a capacity size which is equal or higher then the value that was specified in the PVC.

So if we take this example:

  # PVC
  resources:
     requests:
       storage: 3Gi


  # PV
  capacity:
    storage: 10Gi 

So:
If PV capacity >= PVC capacity then PVC should be bound to PV.

if Not then we'll get the unbound immediate PersistentVolumeClaims error in the pod level and no volume plugin matched name when describing the PVC.

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Example 2

The number of PVC is higher then the PV.

For example if only one PV is created (or the others were deleted):

$ kubectl get pv
NAME             CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                      STORAGECLASS    REASON   AGE
mongo-local-pv   50Gi       RWO            Retain           Bound    default/mongo-persistent-storage-mongo-0   local-storage            106m

We could see that some workloads (Pods or Stateful sets) will be stuck on pending:

$ kubectl get pods
NAME      READY   STATUS    RESTARTS   AGE
mongo-0   2/2     Running   0          3m38s
mongo-1   0/2     Pending   0          3m23s

$ kubectl get pvc
NAME                               STATUS    VOLUME           CAPACITY   ACCESS MODES   STORAGECLASS    AGE
mongo-persistent-storage-mongo-0   Bound     mongo-local-pv   50Gi       RWO            local-storage   80m
mongo-persistent-storage-mongo-1   Pending                                              local-storage   45m

We'll get the mentioned error on the pending resources.

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Example 3

If the scheduler failed to match a node to the PV.

When using local volumes the nodeAffinity of the PV is required and should be a value of an existing node in the cluster:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-mongo-pv
  .
  .
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - node-which-doesnt-exists  # <----- Will lead to the error

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Example 4

Old PVs with the same name and different configuration were already exist on the cluster and the new PVC is created according to them.

When working with local volume the administrator must perform manually clean up and set up the local volume again each time for reuse.

(*) This local static provisioner was created to help with the PV lifecycle.