### 一、简介
PersistentVolume（PV）是指由集群管理员配置提供的某存储系统上的段存储空间，它是对底层共享存储的抽象，将共享存储作为种可由用户申请使的资源，实现了“存储消费”机制。通过存储插件机制，PV支持使用多种网络存储系统或云端存储等多种后端存储系统，例如，NFS、RBD和Cinder等。PV是集群级别的资源，不属于任何名称空间，用户对PV资源的使需要通过PersistentVolumeClaim（PVC）提出的使申请（或称为声明）来完成绑定，是PV资源的消费者，它向PV申请特定大小的空间及访问模式（如rw或ro），从创建出PVC存储卷，后再由Pod资源通过PersistentVolumeClaim存储卷关联使，如下图：
尽管PVC使得用户可以以抽象的方式访问存储资源，但很多时候还是会涉及PV的不少属性，例如，由于不同场景时设置的性能参数等。为此，集群管理员不得不通过多种方式提供多种不同的PV以满不同用户不同的使用需求，两者衔接上的偏差必然会导致用户的需求无法全部及时有效地得到满足。Kubernetes从1.4版起引入了一个新的资源对象StorageClass，可用于将存储资源定义为具有显著特性的类（Class）而不是具体的PV，例如“fast”“slow”或“glod”“silver”“bronze”等。用户通过PVC直接向意向的类别发出申请，匹配由管理员事先创建的PV，或者由其按需为用户动态创建PV，这样做甚至免去了需要先创建PV的过程。
PV对存储系统的支持可通过其插件来实现，目前，Kubernetes支持如下类型的插件。
官方地址：[https://kubernetes.io/docs/concepts/storage/storage-classes/](https://kubernetes.io/docs/concepts/storage/storage-classes/)
由上图我们可以看到官方插件是不支持NFS动态供给的，但是我们可以用第三方的插件来实现，下面就是本文要讲的。
### 二、安装NFS插件
GitHub地址：[https://github.com/kubernetes-incubator/external-storage/tree/master/nfs-client/deploy](https://github.com/kubernetes-incubator/external-storage/tree/master/nfs-client/deploy)
1、下载所需文件
```
for file in class.yaml deployment.yaml rbac.yaml ; do wget https://raw.githubusercontent.com/kubernetes-incubator/external-storage/master/nfs-client/deploy/$file ; done
```
```
# cat rbac.yaml
kind: ServiceAccount
apiVersion: v1
metadata:
name: nfs-client-provisioner
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: nfs-client-provisioner-runner
rules:
- apiGroups: [""]
resources: ["persistentvolumes"]
verbs: ["get", "list", "watch", "create", "delete"]
- apiGroups: [""]
resources: ["persistentvolumeclaims"]
verbs: ["get", "list", "watch", "update"]
- apiGroups: ["storage.k8s.io"]
resources: ["storageclasses"]
verbs: ["get", "list", "watch"]
- apiGroups: [""]
resources: ["events"]
verbs: ["create", "update", "patch"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: run-nfs-client-provisioner
subjects:
- kind: ServiceAccount
name: nfs-client-provisioner
namespace: default
roleRef:
kind: ClusterRole
name: nfs-client-provisioner-runner
apiGroup: rbac.authorization.k8s.io
---
kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: leader-locking-nfs-client-provisioner
rules:
- apiGroups: [""]
resources: ["endpoints"]
verbs: ["get", "list", "watch", "create", "update", "patch"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: leader-locking-nfs-client-provisioner
subjects:
- kind: ServiceAccount
name: nfs-client-provisioner
# replace with namespace where provisioner is deployed
namespace: default
roleRef:
kind: Role
name: leader-locking-nfs-client-provisioner
apiGroup: rbac.authorization.k8s.io
```
3、创建Storageclass类
```
# cat class.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: managed-nfs-storage
provisioner: fuseim.pri/ifs # or choose another name, must match deployment's env PROVISIONER_NAME'
parameters:
archiveOnDelete: "false"
```
4、创建NFS的deployment，修改相应的NFS服务器IP及挂载路径
```
# cat deployment.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
name: nfs-client-provisioner
---
kind: Deployment
apiVersion: apps/v1
metadata:
name: nfs-client-provisioner
spec:
replicas: 1
selector:
matchLabels:
app: nfs-client-provisioner
strategy:
type: Recreate
template:
metadata:
labels:
app: nfs-client-provisioner
spec:
serviceAccountName: nfs-client-provisioner
containers:
- name: nfs-client-provisioner
image: quay.io/external_storage/nfs-client-provisioner:v2.0.0
volumeMounts:
- name: nfs-client-root
mountPath: /persistentvolumes
env:
- name: PROVISIONER_NAME
value: fuseim.pri/ifs
- name: NFS_SERVER
value: 192.168.1.100
- name: NFS_PATH
value: /huoban/k8s
volumes:
- name: nfs-client-root
nfs:
server: 192.168.1.100
path: /huoban/k8s
```
### 三、创建一个PV动态供给应用实例
下面是一个StatefulSet应用动态申请PV的示意图：
例如：创建一个nginx动态获取PV
```
# cat nginx.yaml
---
apiVersion: v1
kind: Service
metadata:
name: nginx
labels:
app: nginx
spec:
ports:
- port: 80
name: web
clusterIP: None
selector:
app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
selector:
matchLabels:
app: nginx
serviceName: "nginx"
replicas: 3
template:
metadata:
labels:
app: nginx
spec:
imagePullSecrets:
- name: huoban-harbor
terminationGracePeriodSeconds: 10
containers:
- name: nginx
image: harbor.huoban.com/open/huoban-nginx:v1.1
ports:
- containerPort: 80
name: web
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: "managed-nfs-storage"
resources:
requests:
storage: 1Gi
```
启动之后我们可以看到一下信息
```
# kubectl get pod,pv,pvc
NAME READY STATUS RESTARTS AGE
pod/nfs-client-provisioner-fcb58977d-l5cs4 1/1 Running 0 20h
pod/web-0 1/1 Running 0 175m
pod/web-1 1/1 Running 0 175m
pod/web-2 1/1 Running 0 175m
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
persistentvolume/default-test-claim-pvc-e5a66781-b46e-4191-8f51-5d1a571ca530 1Mi RWX Delete Bound default/test-claim managed-nfs-storage 20h
persistentvolume/default-www-web-0-pvc-0a578ef2-63e3-49bb-87c0-88166d3e0e65 1Gi RWO Delete Bound default/www-web-0 managed-nfs-storage 20h
persistentvolume/default-www-web-1-pvc-78061eb6-c36b-44db-9472-f2684f85a4b9 1Gi RWO Delete Bound default/www-web-1 managed-nfs-storage 20h
persistentvolume/default-www-web-2-pvc-ec760344-a35a-4048-b8aa-6452d6a62337 1Gi RWO Delete Bound default/www-web-2 managed-nfs-storage 20h
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/test-claim Bound default-test-claim-pvc-e5a66781-b46e-4191-8f51-5d1a571ca530 1Mi RWX managed-nfs-storage 20h
persistentvolumeclaim/www-web-0 Bound default-www-web-0-pvc-0a578ef2-63e3-49bb-87c0-88166d3e0e65 1Gi RWO managed-nfs-storage 20h
persistentvolumeclaim/www-web-1 Bound default-www-web-1-pvc-78061eb6-c36b-44db-9472-f2684f85a4b9 1Gi RWO managed-nfs-storage 20h
persistentvolumeclaim/www-web-2 Bound default-www-web-2-pvc-ec760344-a35a-4048-b8aa-6452d6a62337 1Gi RWO managed-nfs-storage 20h
```
现在，我们在NFS服务器上也可以看到自动生成了3个挂载目录，单pod删除之后数据还会存在
```
# ll
drwxrwxrwx 2 root root 4096 Oct 23 17:31 default-www-web-0-pvc-0a578ef2-63e3-49bb-87c0-88166d3e0e65
drwxrwxrwx 2 root root 4096 Oct 23 17:31 default-www-web-1-pvc-78061eb6-c36b-44db-9472-f2684f85a4b9
drwxrwxrwx 2 root root 4096 Oct 23 17:40 default-www-web-2-pvc-ec760344-a35a-4048-b8aa-6452d6a62337
```
StatefulSet应用有以下特点：
1.唯一的网络标识
2.域名访问(<statefulsetname-index>.<service-name>.svc.cluster.local) 如：web-0.nginx.default.svc.cluster.local/<service-name>/<statefulsetname-index>
3.独立的持久存储
4.有序的部署和删除
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