Persistent Volumes and Persistent Volumes Claims¶

https://kubernetes.io/docs/concepts/storage/persistent-volumes/

Persistent Volumes¶

A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes.

Type of Persistent Volumes

https://kubernetes.io/docs/concepts/storage/persistent-volumes/#types-of-persistent-volumes

Persistent Volumes Claims¶

A request for storage by a user

Size
Access mode (ReadWriteOnce, ReadWriteMany, ReadOnlyMany), access mode is node level access, not pod level
Storage Class

the cluster will map the Persistent Volumes Claim to a Persistent Volume

Static Provisionling Workflow¶

create a PersistentVolume
create a PersistentVolumeClaim
Define Volume in pod spec

Storage Lifecycle¶

Binding (PVC created, match PVC to PV)
Using (pod lifetime)
Reclaim (PVC deleted, the pv will be reclaimed based on the recalimd policy: delete or retain)
- delete, 就是一旦pvc删除了，那么实际这块pv也会被清理，里面的数据会被删除，然后这块空间会等待下一次的pvc
- retain, pvc虽然删除了，但是这块pv里的数据会保留，pv的状态会变为released，这是无法马上被下一次的pvc使用，管理员必须手动清理删除

Define a Persistent Volume¶

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-nfs
spec:
  capacity:
    storage: 4Gi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  nfs:
    server: 192.168.56.20
    path: "/export/volumes/pod"

vagrant@k8s-master:~$ kubectl apply -f pv.yml
persistentvolume/test-nfs created
vagrant@k8s-master:~$ kubectl get persistentvolume
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGE
pv-nfs     4Gi        RWX            Retain           Available                                   5s

Define PersistentVolumeClaim¶

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-nfs
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

Use persistentvolume in Pod¶

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      volumes:
      - name: webcontent
        persistentVolumeClaim:
          claimName: pvc-nfs
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
        volumeMounts:
        - name: webcontent
          mountPath: "/usr/share/nginx/html/web-app"

查看volume mount

$ kubectl get pods -o wide
NAME                  READY   STATUS    RESTARTS   AGE   IP             NODE          NOMINATED NODE   READINESS GATES
web-9996cd57b-988n7   1/1     Running   0          25m   10.244.2.170   k8s-worker2   <none>           <none>

去节点 k8s-worker2 上, 可以看到pod挂载的volume信息

vagrant@k8s-worker2:~$ mount | grep nfs
192.168.56.20:/export/volumes/pod on /var/lib/kubelet/pods/1c17d9be-239c-44b4-8f35-99ad0c7976d2/volumes/kubernetes.io~nfs/pv-nfs type nfs4 (rw,relatime,vers=4.2,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.56.12,local_lock=none,addr=192.168.56.20)

去NFS server上创建一个文件，具体路径为：

vagrant@nfs-server:/export/volumes/pod$ pwd
/export/volumes/pod
vagrant@nfs-server:/export/volumes/pod$ ls
index.html
vagrant@nfs-server:/export/volumes/pod$ more index.html
hello k8s
vagrant@nfs-server:/export/volumes/pod$

创建一个service

$ kubectl expose deployment web --port=80 --type=NodePort
$ kubectl get service
NAME         TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP   10.96.0.1      <none>        443/TCP        25d
web          NodePort    10.97.45.206   <none>        80:32615/TCP   6s

打开浏览器访问 http:<node-ip>:32615/web-app/

应该就能看到 hello k8s

clean¶

$ kubectl delete service web
$ kubectl delete deployments.apps web
$ kubectl delete persistentvolumeclaims pvc-nfs
$ kubectl delete persistentvolume pv-nfs