研发工程师玩转Kubernetes——local型PV和PVC绑定过程中的状态变化

PV全称是PersistentVolume，即持久卷，是由管理员事先准备好的资源。它可以是本地磁盘，也可以是网络磁盘。
PVC全称是PersistentVolumeClaim，即持久卷申领。它表示卷的使用者，对PV的申请。即我们可以认为，PV是整体，PVC是申请其中的部分。

local型PV

local类型的持久卷分配的是本地磁盘空间。K8S要求该类型的卷在配置时指定其节点亲和性（nodeAffinity），即我们优先（只能）在哪些节点上分配空间。

# default_storage_class_pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: default-storage-class-pv
spec:
  capacity:
    storage: 100Ki
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  local:
    path: /tmp
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - ubuntud

accessModes是卷的访问模式。有如下选项：

1. ReadWriteOnce：读写权限，只能被一个Node挂载。
2. ReadOnlyMany：只读权限，可以被多个Node挂载。
3. ReadWriteMany：读写权限，可以被多个Node挂载。

由于上例是本地磁盘，所以只能是ReadWriteOnce，因为它只能被一个Node挂载。
persistentVolumeReclaimPolicy选择Retain，表示资源回收需要手工进行。
local和nodeAffinity表示我们将在ubuntud的/tmp目录下分配卷空间。

静态绑定的PVC

# default_storage_class_pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: default-storage-class-pvc
spec:
  resources:
    requests:
      storage: 10Ki
  volumeName: default-storage-class-pv
  accessModes:
    - ReadWriteOnce

volumeName指定了PV的名称。这样PVC就和PV进行了绑定。

绑定过程中状态的变化

我们创建上述资源PV。

kubectl create -f default_storage_class_pv.yaml 

然后观察其状态：

kubectl describe persistentvolume default-storage-class-pv

Name:              default-storage-class-pv
Labels:            >
Annotations:       >
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      
Status:            Available
Claim:             
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          100Ki
Node Affinity:     
  Required Terms:  
    Term 0:        kubernetes.io/hostname in [ubuntud]
Message:           
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /tmp
Events:    >

可以看到PV处于Available状态。
然后我们创建绑定其的PVC：

kubectl create -f default_storage_class_pvc.yaml 

过段时间后我们查看PVC状态。

kubectl describe persistentvolumeclaims default-storage-class-pvc

Name:          default-storage-class-pvc
Namespace:     default
StorageClass:  
Status:        Bound
Volume:        default-storage-class-pv
Labels:        >
Annotations:   pv.kubernetes.io/bind-completed: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      100Ki
Access Modes:  RWO
VolumeMode:    Filesystem
Used By:       >
Events:        >

可以看到PVC的状态是Bound（已绑定）。
最后我们看下PV的状态，它的状态也变成了Bound（已绑定）。至此，该PV和PVC已经绑定了。

kubectl describe persistentvolume default-storage-class-pv

Name:              default-storage-class-pv
Labels:            >
Annotations:       pv.kubernetes.io/bound-by-controller: yes
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      
Status:            Bound
Claim:             default/default-storage-class-pvc
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          100Ki
Node Affinity:     
  Required Terms:  
    Term 0:        kubernetes.io/hostname in [ubuntud]
Message:           
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /tmp
Events:    >

已经绑定的PV不可以再绑定PVC。我们创建一个新的PVC，进行测试

# default_storage_class_pvc_invalid.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: default-storage-class-pvc-invalid
spec:
  resources:
    requests:
      storage: 10Ki
  volumeName: default-storage-class-pv
  accessModes:
    - ReadWriteOnce

 kubectl create -f default_storage_class_pvc_invalid.yaml

persistentvolumeclaim/default-storage-class-pvc-invalid created

显示创建成功，但是实际状态是Pending。原因是default-storage-class-pv已经绑定到其他PVC。

kubectl describe persistentvolumeclaims default-storage-class-pvc-invalid 

Name:          default-storage-class-pvc-invalid
Namespace:     default
StorageClass:  
Status:        Pending
Volume:        default-storage-class-pv
Labels:        >
Annotations:   >
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      0
Access Modes:  
VolumeMode:    Filesystem
Used By:       >
Events:
  Type     Reason         Age               From                         Message
  ----     ------         ----              ----                         -------
  Warning  FailedBinding  8s (x2 over 22s)  persistentvolume-controller  volume "default-storage-class-pv" already bound to a different claim.

删除过程中的状态变化

我们先删掉上面创建的PVC

kubectl delete persistentvolumeclaims default-storage-class-pvc-invalid
kubectl delete persistentvolumeclaims default-storage-class-pvc

然后观察PV的变化

kubectl describe persistentvolume default-storage-class-pv 

Name:              default-storage-class-pv
Labels:            >
Annotations:       pv.kubernetes.io/bound-by-controller: yes
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      
Status:            Released
Claim:             default/default-storage-class-pvc
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          100Ki
Node Affinity:     
  Required Terms:  
    Term 0:        kubernetes.io/hostname in [ubuntud]
Message:           
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /tmp
Events:    >

此时PV因为绑定的PVC被删除，而其persistentVolumeReclaimPolicy选择了Retain，资源没有被回收，而变成了Released状态。卷的状态如下：

• Available（可用）-- 卷是一个空闲资源，尚未绑定到任何申领；
• Bound（已绑定）-- 该卷已经绑定到某申领；
• Released（已释放）-- 所绑定的申领已被删除，但是资源尚未被集群回收；
• Failed（失败）-- 卷的自动回收操作失败。

这个时候我们再创建上述PVC，还是会处于pending状态。因为PV没有处于Available状态。

kubectl create -f default_storage_class_pvc.yaml

persistentvolumeclaim/default-storage-class-pvc created

kubectl describe persistentvolumeclaims default-storage-class-pvc

Name:          default-storage-class-pvc
Namespace:     default
StorageClass:  
Status:        Pending
Volume:        default-storage-class-pv
Labels:        >
Annotations:   >
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      0
Access Modes:  
VolumeMode:    Filesystem
Used By:       >
Events:
  Type     Reason         Age   From                         Message
  ----     ------         ----  ----                         -------
  Warning  FailedBinding  8s    persistentvolume-controller  volume "default-storage-class-pv" already bound to a different claim.

再绑定Released状态的PV

使用下面指令，删除描述绑定信息的claimRef段。

kubectl edit persistentvolume default-storage-class-pv

# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
kind: PersistentVolume
metadata:
  annotations:
    pv.kubernetes.io/bound-by-controller: "yes"
  creationTimestamp: "2023-08-09T09:26:04Z"
  finalizers:
  - kubernetes.io/pv-protection
  name: default-storage-class-pv
  resourceVersion: "285190"
  uid: 09782be4-09b9-4116-9b44-8dbb75f08dbf
spec:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 100Ki
  claimRef:
    apiVersion: v1
    kind: PersistentVolumeClaim
    name: default-storage-class-pvc
    namespace: default
    resourceVersion: "285153"
    uid: c55398f4-77cd-4627-8a11-57b0e049c594
  local:
    path: /tmp
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - ubuntud
  persistentVolumeReclaimPolicy: Retain
  volumeMode: Filesystem
status:
  phase: Released

保存完后过一会儿，PV就会变成Available状态。而之前处于Pending状态的PVC也会因为PV的状态变化从Pending变成Bound状态，PV也会进而变成Bound状态

kubectl describe persistentvolume default-storage-class-pv 

Name:              default-storage-class-pv
Labels:            >
Annotations:       pv.kubernetes.io/bound-by-controller: yes
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      
Status:            Bound
Claim:             default/default-storage-class-pvc
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          100Ki
Node Affinity:     
  Required Terms:  
    Term 0:        kubernetes.io/hostname in [ubuntud]
Message:           
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /tmp
Events:    >

kubectl describe persistentvolumeclaims default-storage-class-pvc

Name:          default-storage-class-pvc
Namespace:     default
StorageClass:  
Status:        Bound
Volume:        default-storage-class-pv
Labels:        >
Annotations:   pv.kubernetes.io/bind-completed: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      100Ki
Access Modes:  RWO
VolumeMode:    Filesystem
Used By:       >
Events:        >

参考资料

• https://kubernetes.io/zh-cn/docs/concepts/storage/persistent-volumes/
• https://cloud.tencent.com/document/product/457/47014