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Azure Kubernetes Service–Volume node affinity conflict

When trying to deploy a pod on our AKS cluster, it hanged in the pending state. I looked at the logs and noticed the following warning:

FailedScheduling – 1 node(s) had volume node affinity conflict

The pod I tried to deploy had a persistent volume claim and I was certain that the persistent volume was succesfully deployed and available.

What was going wrong?

It turned out that my AKS cluster was deployed in 3 availability zones but I had only 2 nodes running:

AKS cluster is gedeployed in 3 zones maar er zijn maar 2 nodes:

$ kubectl describe nodes | grep -e "Name:" -e "failure-domain.beta.kubernetes.io/zone"

Name:               aks-agentpool-38609413-vmss000003

                    failure-domain.beta.kubernetes.io/zone=westeurope-1

Name:               aks-agentpool-38609413-vmss000004

                    failure-domain.beta.kubernetes.io/zone=westeurope-2

Here we can see that our nodes are living in zones westeurope-1 and westeurope-2.

If we now take a look at our persistent volume, we can see that it is deployed in zone westeurope-3:

$  kubectl describe pv pvc-ecc

                   failure-domain.beta.kubernetes.io/zone=westeurope-3

Annotations:       pv.kubernetes.io/bound-by-controller: yes

                   pv.kubernetes.io/provisioned-by: kubernetes.io/azure-disk

                   volumehelper.VolumeDynamicallyCreatedByKey: azure-disk-dynamic-provisioner

Finalizers:        [kubernetes.io/pv-protection]

StorageClass:      default

Status:            Bound

Claim:             appservice-ns/appservice-ext-k8se-build-service

Reclaim Policy:    Delete

Access Modes:      RWO

VolumeMode:        Filesystem

Capacity:          100Gi

Node Affinity:

  Required Terms:

    Term 0:        failure-domain.beta.kubernetes.io/region in [westeurope]

                   failure-domain.beta.kubernetes.io/zone in [westeurope-3]

Message:

That explains why the deployment failed as the pod cannot connect to the volume on another zone.

As a quick solution I introduced a 3th node in the cluster so that at least one node can connect to the persistent volume.

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