Kubernets Storage Demos

In my previous post, shows the basic concepts for Storage in kubernetes, here I want to use some simplified demos to show how these concepts exactly used in a cluster.

Here we use one Emphemral volume -- HostPath type, and a Persistent Volume -- local type as two examples:

HostPath Type

HostPath Type is an empheral volume, even if it will keep the stored file after Pod deleted.

Main Difference:

• No PVC, directly bound with Pod
• Manually create affinity for Pod

apiVersion: v1
kind: PersistentVolume
metadata:
  name: hostpath-pv
spec:
  capacity:
    storage: 100Mi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: /mnt/data # if not exist will create

---
apiVersion: v1
kind: Pod
metadata:
  name: pod-using-hostpath
spec:
  affinity:
    nodeAffinity: # host path should have the nodeAffinity item
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
              - node01
  volumes:
    - name: hostpath-volume
      hostPath:
        path: /mnt/data
  containers:
    - name: app
      image: busybox
      command: ["sleep", "3600"]
      volumeMounts:
        - mountPath: /data
          name: hostpath-volume

Local Type

local type is Persistent Volume type, therefore we need create a PVC, and also with a StorageClass.

Main Difference:

• PVC
• SC
• PV need nodeAffinity
• Pod will be assigned according to the node of PV automatically

apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-pv
spec:
  capacity:
    storage: 100Mi
  accessModes:
    - ReadWriteOnce
  storageClassName: local-storage # just a template
  local:
    path: /mnt/data # this should exist
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - node01

---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: local-pvc
spec:
  storageClassName: local-storage
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 50Mi


---
apiVersion: v1
kind: Pod
metadata:
  name: pod-using-local
spec:
  volumes:
    - name: local-volume
      persistentVolumeClaim:
        claimName: local-pvc
  containers:
    - name: app
      image: busybox
      command: ["sleep", "3600"]
      volumeMounts:
        - mountPath: /data
          name: local-volume

Reuse the PV

If we have delete the PV, but still want to continue using the content stored, we need to specify the claimRef field and make sure the persistentVolumeReclaimPolicy field is Retain (for local type the official documnet DON'T recommend set persistentVolumeReclaimPolicy: Delete.
for more details of reuse the PV, pls check the official documents: here.