在《研发工程师玩转Kubernetes——local型PV和PVC绑定过程中的状态变化》和《研发工程师玩转Kubernetes——使用local型PV在不同Pod上共享数据》中，我们介绍了指定VPC的spec.volumeName为PV名称来绑定它们的方法。本文将介绍PVC在创建时，系统自动选择绑定哪个PV。
在设计上，PV是系统管理员分配的，它用于隔绝具体是哪种介质。比如一些PV来源于谷歌云，一些PV来源于阿里云，还有一些PV来源于AWS。

使用者只要通过PVC向其申请使用即可。

申请时可以通过spec.volumeName指定特定名称PV，还可以使用spec.selector在一堆PV中选择符合条件的PV。

创建多个PV

我们分别使用下面三个配置创建storage为256K、512K和1M的PV。它们都有名字是volume，值是lb-default-storage-class-pv的label。

# default_storage_class_pv_256k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: default-storage-class-pv-256klabels:volume: lb-default-storage-class-pv
spec:capacity:storage: 256KivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: Retainlocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

# default_storage_class_pv_512k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: default-storage-class-pv-256klabels:volume: lb-default-storage-class-pv
spec:capacity:storage: 512KivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: Retainlocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

# default_storage_class_pv_1024k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: default-storage-class-pv-256klabels:volume: lb-default-storage-class-pv
spec:capacity:storage: 1MivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: Retainlocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

创建带选择功能的PVC

PVC申请的空间是600K，介于512K和1M。

# default_storage_class_pvc_600k.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:name: default-storage-class-pvc-600k
spec:resources:requests:storage: 600KiaccessModes:- ReadWriteOnceselector:matchLabels:volume: lb-default-storage-class-pv

创建之后，我们查看该PVC的信息。

kubectl describe persistentvolumeclaims default-storage-class-pvc-600k 

Name:          default-storage-class-pvc-600k
Namespace:     default
StorageClass:  
Status:        Bound
Volume:        default-storage-class-pv-1024k
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yespv.kubernetes.io/bound-by-controller: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      1Mi
Access Modes:  RWO
VolumeMode:    Filesystem
Used By:       <none>
Events:        <none>

可以看到，因为这三个PV的Label都符合PVC的选择器。但是由于256K和512K的PV都小于600K的要求，于是它只能选择最接近它的1M大小的PV。

不匹配的Label

我们创建一个Label不匹配的PVC清单，并创建它。

# default_storage_class_pvc_100k_not_match.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:name: default-storage-class-pvc-100k-not-match
spec:resources:requests:storage: 100KiaccessModes:- ReadWriteOnceselector:matchLabels:volume: lb-default-storage-class-pv-not-match

可以看到它一直处于Pending状态，因为没有符合Label要求的PV。

kubectl describe persistentvolumeclaims default-storage-class-pvc-100k-not-match

Name:          default-storage-class-pvc-100k-not-match
Namespace:     default
StorageClass:  
Status:        Pending
Volume:        
Labels:        <none>
Annotations:   <none>
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      
Access Modes:  
VolumeMode:    Filesystem
Used By:       <none>
Events:Type    Reason         Age               From                         Message----    ------         ----              ----                         -------Normal  FailedBinding  5s (x2 over 11s)  persistentvolume-controller  no persistent volumes available for this claim and no storage class is set

无法满足大小的PVC

之前创建的600K大小的default-storage-class-pvc-600k已经把default-storage-class-pv-256k占用了，只剩下512K和256K大小的PV。
我们再创建一个不满足剩余PV大小的PVC。

# default_storage_class_pvc_700k.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:name: default-storage-class-pvc-700k
spec:resources:requests:storage: 700KiaccessModes:- ReadWriteOnceselector:matchLabels:volume: lb-default-storage-class-pv

观察其状态，可以发现其也处于Pending状态。

kubectl describe persistentvolumeclaims default-storage-class-pvc-700k 

Name:          default-storage-class-pvc-700k
Namespace:     default
StorageClass:  
Status:        Pending
Volume:        
Labels:        <none>
Annotations:   <none>
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      
Access Modes:  
VolumeMode:    Filesystem
Used By:       <none>
Events:Type    Reason         Age              From                         Message----    ------         ----             ----                         -------Normal  FailedBinding  8s (x2 over 9s)  persistentvolume-controller  no persistent volumes available for this claim and no storage class is set

延迟绑定

对于处于Pending状态的PVC，只要我们创建符合条件的PV，系统就会自动将其绑定。
创建下面的PV，它大小是2M，可以满足上面700K请求空间的PVC。

# default_storage_class_pv_2m.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: default-storage-class-pv-2048klabels:volume: lb-default-storage-class-pv
spec:capacity:storage: 2MivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: Retainlocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

然后再观察之前处于Pending状态的PVC状态。可以看到其变成了Bound状态，且其绑定的PV就是刚创建的符合其条件的default-storage-class-pv-2048k。

kubectl describe persistentvolumeclaims default-storage-class-pvc-700k

Name:          default-storage-class-pvc-700k
Namespace:     default
StorageClass:  
Status:        Bound
Volume:        default-storage-class-pv-2048k
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yespv.kubernetes.io/bound-by-controller: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      2Mi
Access Modes:  RWO
VolumeMode:    Filesystem
Used By:       <none>
Events:Type    Reason         Age                     From                         Message----    ------         ----                    ----                         -------Normal  FailedBinding  2m36s (x26 over 8m37s)  persistentvolume-controller  no persistent volumes available for this claim and no storage class is set