concept PersistentVolume in category kubernetes

This is an excerpt from Manning's book Kubernetes in Action. Login to get full access to this book.

Using a PersistentVolume inside a pod is a little more complex than using a regular pod volume, so let’s illustrate how pods, PersistentVolumeClaims, PersistentVolumes, and the actual underlying storage relate to each other in figure 6.6.

Figure 6.6. PersistentVolumes are provisioned by cluster admins and consumed by pods through PersistentVolumeClaims.

Instead of the developer adding a technology-specific volume to their pod, it’s the cluster administrator who sets up the underlying storage and then registers it in Kubernetes by creating a PersistentVolume resource through the Kubernetes API server. When creating the PersistentVolume, the admin specifies its size and the access modes it supports.

You can also see that the PersistentVolume is now Bound and no longer Available by inspecting it with kubectl get:

$ kubectl get pv
NAME         CAPACITY   ACCESSMODES   STATUS   CLAIM                 AGE
mongodb-pv   1Gi        RWO,ROX       Bound    default/mongodb-pvc   1m


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The PersistentVolume shows it’s bound to claim default/mongodb-pvc. The default part is the namespace the claim resides in (you created the claim in the default namespace). We’ve already said that PersistentVolume resources are cluster-scoped and thus cannot be created in a specific namespace, but PersistentVolumeClaims can only be created in a specific namespace. They can then only be used by pods in the same namespace.