Dynamic Disk provisioning with Kubernetes
Kubernetes can automatically provision PersistentVolume for you and make them available for your PersistentVolumes.
This can be helpful if you are for example in a cloud provider like Azure.
You need the interaction between the StorageClass, PersistentVolumeClaim and Pod resources to make it work.
The StorageClass resource
For this you need to create a StorageClass resource which describes the classes of storages you offer.
You can list your available StorageClass resources via the following command:
kubectl get sc
The StorageClass resource looks like the following:
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: managed-premium-retain
provisioner: disk.csi.azure.com
parameters:
skuName: Premium_LRS
reclaimPolicy: Retain
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
Significant fields are name and provisioner.
The name field will be referenced later in your PersistentVolumeClaim and trigger the provisioning.
The provisioner field describes the provisioner which is responsible for the provisioning of the PersistentVolume.
Things to know about the StorageClasses:
- There are built-in StorageClasses in some managed Kubernetes clusters, so you don’t necessary need to define your storage class!
- There are built-in provisioners.
- You can also use external provisioners.
The PersistentVolumeClaim resource
Within the PersistentVolumeClaim you reference the name of the StorageClass:
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: azure-managed-disk
spec:
accessModes:
- ReadWriteOnce
storageClassName: managed-premium-retain
resources:
requests:
storage: 5Gi
With this a PersistentVolume is provisioned and bound to the PersistentVolumeClaim. They are mapped 1:1 to claims.
The Pod resource
In the Pod resource the persistentVolumeClaim is referenced throguh it’s name:
kind: Pod
apiVersion: v1
metadata:
name: nginx
spec:
containers:
- name: myfrontend
image: mcr.microsoft.com/oss/nginx/nginx:1.15.5-alpine
volumeMounts:
- mountPath: "/mnt/azure"
name: volume
volumes:
- name: volume
persistentVolumeClaim:
claimName: azure-managed-disk
The claim can be referenced through the volumeMounts field in the Pod.