<aside> 💡 Persistent Volume(PV) & Persistent Volume Claim(PVC)，透過這兩個概念將連結 storage 的過程抽象化

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PersistentVolume

PersistentVolume 是一個 Storage 的抽象物件，可以由管理者直接提供，或是由 StorageClass 來動態產生。PersistentVolume 跟 Volume 類似，但是 PersistentVolume 的 Lifecycle 獨立的，也就是當與其綁定的 Pod 消失時，PersistentVolume 不一定會跟著消失。

Define a PersistentVolume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0003
spec:
  capacity:
    storage: 5Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Recycle
  storageClassName: slow
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /tmp
    server: 172.17.0.2

Capacity → 容量
VolumeMode → FileSystem / Block
AccessMode →
- ReadWriteOnce → the volume can be mounted as read-write by a single node
- ReadOnlyMany → the volume can be mounted read-only by many nodes
- ReadWriteMany → the volume can be mounted as read-write by many nodes
PersistentVolumeReclaimPolicy →
- Retain → manual reclamation
- Recycle → basic scrub (rm -rf /thevolume/*)
- Delete → associated storage asset such as AWS EBS, GCE PD, Azure Disk, or OpenStack Cinder volume is deleted

PersistentVolumeClaim

PersistentVolumeClaim 是用來 **Request Storage (PersistentVolume)，**若 PersistentVolume 不存在，要求 StorageClass 建造 PersistentVolume，否則 PersistentVolumeClaim 會一直在 Unbound State。

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  resources:
    requests:
      storage: 8Gi
  storageClassName: slow
  selector:
    matchLabels:
      release: "stable"
    matchExpressions:
      - {key: environment, operator: In, values: [dev]}

selector → 篩選 PersistentVolume 用
storageClassName → 篩選 StorageClass 用。
resources.requests.storage → 要求的大小， PersistentVolume 的大小不一定等於 resources.requests.storage，但是一定大於。

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
    - name: myfrontend
      image: nginx
      volumeMounts:
      - mountPath: "/var/www/html"
        name: mypd
  volumes:
    - name: mypd
      persistentVolumeClaim:
        claimName: myclaim

volumes.persistentVolumeClaim → 指定 PersistentVolumeClaim 的名字
spec.containers[].volumeMounts.mountPath → 檔案綁定在 PersistentVolume 中的位置。

StorageClass

用於動態的產生新的 PersistentVolume 給 PersistentVolumeClaim 使用。

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: managed-nfs-storage
provisioner: nthu.laslab.com/nfs
parameters:
  archiveOnDelete: "false"