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: 512Ki
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Delete
storageClassName: local-storage-class-immediate
local:
path: /tmp
nodeAffinity:
required:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- ubuntud
# local_storage_class_immediate_pv_1024k.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: local-storage-class-immediate-pv-1024k
spec:
capacity:
storage: 1024Ki
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Delete
storageClassName: local-storage-class-immediate
local:
path: /tmp
nodeAffinity:
required:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- 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: 600Ki
accessModes:
- ReadWriteOnce
storageClassName: 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-1024k
labels:
volume: lb-default-storage-class-pv
spec:
capacity:
storage: 1Mi
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Retain
local:
path: /tmp
nodeAffinity:
required:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- 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: >
Annotations: pv.kubernetes.io/bind-completed: yes
pv.kubernetes.io/bound-by-controller: yes
Finalizers: [kubernetes.io/pvc-protection]
Capacity: 1Mi
Access Modes: RWO
VolumeMode: Filesystem
Used By: >
Events: >
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: 600Ki
accessModes:
- ReadWriteOnce
storageClassName: 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: >
Annotations: >
Finalizers: [kubernetes.io/pvc-protection]
Capacity:
Access Modes:
VolumeMode: Filesystem
Used By: >
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: >
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: >