Persistent Volume
A persistent volume is a piece of storage in a Kubernetes cluster. PersistentVolumes are a cluster-level resource like nodes, which don't belong to any namespace. It is provisioned by the administrator and has a particular file size. This way, a developer deploying their app on Kubernetes need not know the underlying infrastructure. When the developer needs a certain amount of persistent storage for their application, the system administrator configures the cluster so that they consume the PersistentVolume provisioned in an easy way.
Creating Persistent Volume
kind: PersistentVolume
apiVersion: v1
metadata:
name:app-data
spec:
capacity: # defines the capacity of PV we are creating
storage: 2Gi #the amount of storage we are tying to claim
accessModes: # defines the rights of the volume we are creating
- ReadWriteMany
hostPath:
path: "/srv/app-data" # path to which we are creating the volume
Challenge
* Create a Persistent Volume named app-data, with access mode ReadWriteMany, storage classname shared, 2Gi of storage capacity and the host path /srv/app-data.
2. Save the file and create the persistent volume.
Image for post
3. View the persistent volume.
* Our persistent volume status is available meaning it is available and it has not been mounted yet. This status will change when we mount the persistentVolume to a persistentVolumeClaim.
PersistentVolumeClaim
In a real ecosystem, a system admin will create the PersistentVolume then a developer will create a PersistentVolumeClaim which will be referenced in a pod. A PersistentVolumeClaim is created by specifying the minimum size and the access mode they require from the persistentVolume.
Challenge
* Create a Persistent Volume Claim that requests the Persistent Volume we had created above. The claim should request 2Gi. Ensure that the Persistent Volume Claim has the same storageClassName as the persistentVolume you had previously created.
kind: PersistentVolume
apiVersion: v1
metadata:
name:app-data
spec:
accessModes:
- ReadWriteMany
resources:
requests:
storage: 2Gi
storageClassName: shared
2. Save and create the pvc
njerry191@cloudshell:~ (extreme-clone-2654111)$ kubect1 create -f app-data.yaml persistentvolumeclaim/app-data created
3. View the pvc
Image for post
4. Let's see what has changed in the pv we had initially created.
Image for post
Our status has now changed from available to bound.
5. Create a new pod named myapp with image nginx that will be used to Mount the Persistent Volume Claim with the path /var/app/config.
Mounting a Claim
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
name: app-data
spec:
volumes:
- name:congigpvc
persistenVolumeClaim:
claimName: app-data
containers:
- image: nginx
name: app
volumeMounts:
- mountPath: "/srv/app-data "
name: configpvc
