研发工程师玩转Kubernetes——PVC使用storageClassName选择PV

除了《研发工程师玩转Kubernetes——PVC使用Label和storage选择PV》中介绍的使用Label做选择因子外，PVC还可以通过storageClassName选择符合条件的PV。
StorageClass的设计是用于描述如何动态创建PV。最开始时，管理员需要一次性申请好所有的PV，使用者只要设计PVC申请PV绑定即可。但是如果一旦PV不够用了，管理员又要手工去申请PV来满足需求。为了降低管理员的工作，StorageClass可以动态去创建PV，即PVC发现PV不够后，直接通过其指定的storageClassName来动态创建PV。
本文只介绍PVC如何使用storageClassName选择已经创建好的PV。

StorageClass清单

# local_storage_class_immediate.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:name: local-storage-class-immediate
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: Immediate

我们创建了一个名字叫local-storage-class，使用本地存储的StorageClass。它的绑定类型是Immediate（立即）。Immediate 模式表示一旦创建了 PersistentVolumeClaim 也就完成了卷绑定。

PV清单

这次我们创建的PV没有设置Label，而是设置了storageClassName字段为上述StorageClass的名字。

# local_storage_class_immediate_pv_512k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: local-storage-class-immediate-pv-512k
spec:capacity:storage:  512KivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: DeletestorageClassName: local-storage-class-immediatelocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

# local_storage_class_immediate_pv_1024k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: local-storage-class-immediate-pv-1024k
spec:capacity:storage:  1024KivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: DeletestorageClassName: local-storage-class-immediatelocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

PVC清单

这个清单也没使用spec.selector对PV的Label做选择，而是使用了storageClassName。

# local_storage_class_immediate_pvc_600k.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:name: local-storage-class-immediate-pvc-600k
spec:resources:requests:storage: 600KiaccessModes:- ReadWriteOncestorageClassName: local-storage-class-immediate

测试

为了验证测试，我们同时创建下面这个PV，它只是在storage上满足上述PVC申请。

# default_storage_class_pv_1024k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:name: default-storage-class-pv-1024klabels:volume: lb-default-storage-class-pv
spec:capacity:storage: 1MivolumeMode: FilesystemaccessModes:- ReadWriteOncepersistentVolumeReclaimPolicy: Retainlocal:path: /tmpnodeAffinity:required:nodeSelectorTerms:- matchExpressions:- key: kubernetes.io/hostnameoperator: Invalues:- ubuntud

使用下面指令创建上述资源

kubectl create -f local_storage_class_immediate.yaml -f default_storage_class_pv_1024k.yaml  -f local_storage_class_immediate_pv_1024k.yaml -f local_storage_class_immediate_pv_512k.yaml -f local_storage_class_immediate_pvc_600k.yaml

查看PVC的状态，可以发现系统让storageClassName名相同的PV和PVC进行了绑定。

kubectl describe persistentvolumeclaims  local-storage-class-immediate-pvc-600k

Name:          local-storage-class-immediate-pvc-600k
Namespace:     default
StorageClass:  local-storage-class-immediate
Status:        Bound
Volume:        local-storage-class-immediate-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>

为了进一步测试，我们再创建相同配置，但是名字不同的PVC，看它是否会选择没有设置相同storageClassName的PV。

apiVersion: v1
kind: PersistentVolumeClaim
metadata:name: local-storage-class-immediate-pvc-600k-1
spec:resources:requests:storage: 600KiaccessModes:- ReadWriteOncestorageClassName: local-storage-class-immediate

kubectl describe persistentvolumeclaims local-storage-class-immediate-pvc-600k-1

Name:          local-storage-class-immediate-pvc-600k-1
Namespace:     default
StorageClass:  local-storage-class-immediate
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----     ------              ----  ----                         -------Warning  ProvisioningFailed  6s    persistentvolume-controller  no volume plugin matched name: kubernetes.io/no-provisioner

可以看到即使storage满足PVC申请的大小，但是由于storageClassName不同，它还是没有选择default-storage-class-pv-1024k这个PV。

kubectl describe persistentvolume default-storage-class-pv-1024k

Name:              default-storage-class-pv-1024k
Labels:            volume=lb-default-storage-class-pv
Annotations:       <none>
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      
Status:            Available
Claim:             
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          1Mi
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:    <none>