### 一、簡介
PersistentVolume（PV）是指由集群管理員配置提供的某存儲系統上的段存儲空間，它是對底層共享存儲的抽象，將共享存儲作為種可由用戶申請使的資源，實現了“存儲消費”機制。通過存儲插件機制，PV支持使用多種網絡存儲系統或雲端存儲等多種後端存儲系統，例如，NFS、RBD和Cinder等。PV是集群級別的資源，不屬於任何名稱空間，用戶對PV資源的使需要通過PersistentVolumeClaim（PVC）提出的使申請（或稱為聲明）來完成綁定，是PV資源的消費者，它向PV申請特定大小的空間及訪問模式（如rw或ro），從創建出PVC存儲卷，後再由Pod資源通過PersistentVolumeClaim存儲卷關聯使，如下圖：
儘管PVC使得用戶可以以抽象的方式訪問存儲資源，但很多時候還是會涉及PV的不少屬性，例如，由於不同場景時設置的性能參數等。為此，集群管理員不得不通過多種方式提供多種不同的PV以滿不同用戶不同的使用需求，兩者銜接上的偏差必然會導致用戶的需求無法全部及時有效地得到滿足。Kubernetes從1.4版起引入了一個新的資源對象StorageClass，可用於將存儲資源定義為具有顯著特性的類（Class）而不是具體的PV，例如“fast”“slow”或“glod”“silver”“bronze”等。用戶通過PVC直接向意向的類別發出申請，匹配由管理員事先創建的PV，或者由其按需為用戶動態創建PV，這樣做甚至免去了需要先創建PV的過程。
PV對存儲系統的支持可通過其插件來實現，目前，Kubernetes支持如下類型的插件。
官方地址：[https://kubernetes.io/docs/concepts/storage/storage-classes/](https://kubernetes.io/docs/concepts/storage/storage-classes/)
由上圖我們可以看到官方插件是不支持NFS動態供給的，但是我們可以用第三方的插件來實現，下面就是本文要講的。
### 二、安裝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、下載所需文件
```
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、創建Storageclass類
```
# 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、創建NFS的deployment，修改相應的NFS服務器IP及掛載路徑
```
# 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、創建一個PV動態供給應用實例
下面是一個StatefulSet應用動態申請PV的示意圖：
例如：創建一個nginx動態獲取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
```
啟動之後我們可以看到一下信息
```
# 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
```
現在，我們在NFS服務器上也可以看到自動生成了3個掛載目錄，單pod刪除之後數據還會存在
```
# 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應用有以下特點：
1.唯一的網絡標識
2.域名訪問(<statefulsetname-index>.<service-name>.svc.cluster.local) 如：web-0.nginx.default.svc.cluster.local/<service-name>/<statefulsetname-index>
3.獨立的持久存儲
4.有序的部署和刪除
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