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Volumes, PV & PVC

  • The pod doesn’t talk directly to a PV — it uses a PVC, which in turn is bound to a PV.
    • PVC is a contract between PV and the pod.
  • A PersistentVolume can be created standalone, without binding.
  • A PVC does not have to name a PV. Kubernetes will bind it automatically to a suitable PV (manual binding is also possible but uncommon).
  • A Pod uses a PVC to claim access to storage — the Pod never uses a PV directly.
  • PV to PVC binding is one to one, always.
  • One PVC can be used by many Pods if the mode allows.

Pod using PV

apiVersion: v1
kind: Pod
metadata:
  name: random-number-gen
spec:
  containers:
  - name: alpine
    image: alpine
    command: ["/bin/sh", "-c"]
    args: ["shuf -i 0-100 -n 1 >> /opt/number.out && sleep 3600"]
    volumeMounts:
    - mountPath: /opt
      name: data-volume
  volumes:
  - name: data-volume
    hostPath:
      path: /data
      type: Directory
  - name: myPd
    persistentVolumeClaim:
      claimName: myclaim

Persistent Volume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-vol1
spec:
  accessModes:
  - ReadWriteOnce
  capacity: 
    storage: 1Gi
  hostPath:
    path: "/pv/log"
  awsElasticBlockStore:
    volumeID: <id>
    fsType: ext4
  persistentVolumeReclaimPolicy: Retain

Persistent Volume Providers

NFS, GlusterFS, Flocker, ceph, ScaleIO, aws, gcp...

PVC​

PersistentVolumeClaim

k get persistentvolumeclaim # pvc
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
	name: myclaim
spec:
	accessModes:
	- ReadWriteOnce
	resources:
		requests:
			storage: 500mi

Storage Class​

StorageClass
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: cloud-storage
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
  fsType: ext4
reclaimPolicy: Retain
allowVolumeExpansion: true
volumeBindingMode: Immediate|WaitForFirstConsumer
PVC with storage class
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: cloud-storage
  resources:
    requests:
      storage: 10Gi