Kubernetes数据持久化之StatefulSet（自动创建PVC）

一、Kubernetes无状态服务VS有状态服务

1）Kubernetes无状态服务

Kubernetes无状态服务特征：
1）是指该服务运行的实例不会在本地存储需要持久化的数据，并且多个实例对于同一请求响应的结果是完全一致的；
2）多个实例可以共享相同的持久化数据。例如：nginx实例、tomcat实例等；
3）相关的Kubernetes资源有：ReplicaSet、ReplicationController、Deployment等，由于是无状态服务，所以这些控制器创建的Pod名称都是随机性的。并且在缩容时并不会明确缩容某一个Pod，而是随机的，因为所有实例得到的返回值都是一样的，所以缩容任何一个Pod都可以；

2）Kubernetes有状态服务

Kubernetes有状态服务特征：
1）有状态服务可以说是需要数据存储功能的服务、或者指多线程类型的服务、队列等。（比如：mysql数据库、kafka、zookeeper等）；
2）每个实例都需要自己独立的持久化存储，并且在Kubernetes中通过声明模板的方式来进行定义。持久卷声明模板在创建pod之前创建，绑定到pod中，模板可以定义多个；
3）相关的Kubernetes资源有：StatefulSet。由于是有状态的服务，所以每个Pod都有特定的名称和网络标识。比如Pod名称是由StatefulSet名+有序的数字组成（0、1、2……）；
4）在进行缩容操作时，可以明确知道会缩容那一个Pod，从数字最大的开始。并且StatefulSet在已有实例不健康的情况下是不允许做缩容操作的；

3）无状态服务和有状态服务的区别

主要表现在以下方面：
1）实例数量：无状态服务可以有一个或多个实例，因此支持两种服务容量调节模式；有状态服务职能有一个实例，不允许创建多个实例，因此也不支持服务容量的调节；
2）存储卷：无状态服务可以有存储卷，也可以没有，即使有也无法备份存储卷中的数据；有状态服务必须要有存储卷，并且在创建服务时，必须指定该存储卷分配的磁盘空间大小；
3）数据存储：
无状态服务运行过程中的所有数据（除日志和监控数据）都存在容器实例里的文件系统中，如果实例停止或者删除，则这些数据都将丢失，无法找回；而对于有状态服务，凡是已经挂载了存储卷的目录下的文件内容都可以随时进行备份，备份的数据可以下载，也可以用于恢复新的服务。但对于没有挂载卷的目录下的数据，仍然是无法备份和保存的，如果实例停止或者删除，这些非挂载卷里的文件内容同样会丢失。

4）StatefulSet概述
StatefulSet是Kubernetes提供的管理有状态应用的负载管理控制器API。在Pods管理的基础上，保证Pods的顺序和一致性。与Deployment一样，StatefulSet也是使用容器的Spec来创建Pod，与之不同StatefulSet创建的Pods在生命周期中会保持持久的标记（例如Pod Name）。

5）StatefulSet特点

1）稳定的持久化存储，即Pod重新调度后还是能访问到相同的持久化数据，基于PVC来实现；
2）稳定的网络标志，即Pod重新调度后其PodName和HostName不变，基于Headless Service（即没有Cluster IP的Service）来实现；
3）有序部署，有序扩展，即Pod是有顺序的，在部署或者扩展的时候要依据定义的顺序依次依次进行（即从0到N-1，在下一个Pod运行之前所有之前的Pod必须都是Running和Ready状态），基于init containers来实现；
4）有序收缩，有序删除（即从N-1到0）；

二、使用StatefulSet实现自动创建PVC

1）搭建NFS共享存储
为了方便，就直接在master节点上部署NFS存储了！

[root@master ~]# yum -y install nfs-utils rpcbind
[root@master ~]# vim /etc/exports
/nfsdata *(rw,sync,no_root_squash)
[root@master ~]# mkdir /nfsdata
[root@master ~]# systemctl start nfs-server
[root@master ~]# systemctl start rpcbind
[root@master ~]# showmount -e
Export list for master:
/nfsdata *

2）创建rbac授权

[root@master ~]# vim rbac-rolebind.yaml
apiVersion: v1                            #创建一个用于认证的服务账号
kind: ServiceAccount
metadata:
  name: nfs-provisioner
---
apiVersion: rbac.authorization.k8s.io/v1        #创建群集规则
kind: ClusterRole
metadata:
  name: nfs-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: ["watch", "create", "update", "patch"]
   -  apiGroups: [""]
      resources: ["services", "endpoints"]
      verbs: ["get","create","list", "watch","update"]
   -  apiGroups: ["extensions"]
      resources: ["podsecuritypolicies"]
      resourceNames: ["nfs-provisioner"]
      verbs: ["use"]
---
kind: ClusterRoleBinding                #将服务认证用户与群集规则进行绑定
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: run-nfs-provisioner
subjects:
  - kind: ServiceAccount
    name: nfs-provisioner
    namespace: default                    #必写字段，否则会提示错误
roleRef:
  kind: ClusterRole
  name: nfs-provisioner-runner
  apiGroup: rbac.authorization.k8s.io
[root@master ~]# kubectl apply -f rbac-rolebind.yaml 

3）创建nfs-deployment.资源

[root@master ~]# vim nfs-deployment.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nfs-client-provisioner
spec:
  replicas: 1                              #指定副本数量为1
  strategy:
    type: Recreate                      #指定策略类型为重置
  template:
    metadata:
      labels:
        app: nfs-client-provisioner
    spec:
      serviceAccount: nfs-provisioner            #指定rbac yanl文件中创建的认证用户账号
      containers:
        - name: nfs-client-provisioner
          image: registry.cn-hangzhou.aliyuncs.com/open-ali/nfs-client-provisioner     #使用的镜像 
          volumeMounts:
            - name: nfs-client-root
              mountPath:  /persistentvolumes             #指定容器内挂载的目录
          env:
            - name: PROVISIONER_NAME           #容器内的变量用于指定提供存储的名称
              value: zjz
            - name: NFS_SERVER                      #容器内的变量用于指定nfs服务的IP地址
              value: 192.168.10.52
            - name: NFS_PATH                       #容器内的变量指定nfs服务器对应的目录
              value: /nfsdata
      volumes:                                                #指定挂载到容器内的nfs的路径及IP
        - name: nfs-client-root
          nfs:
            server: 192.168.10.52
            path: /nfsdata
[root@master ~]# kubectl apply -f nfs-deployment.yaml
[root@master ~]# kubectl get pod 
NAME                                      READY   STATUS    RESTARTS   AGE
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running   0          44s

4）创建SC（Storage Class）

[root@master ~]# vim sc.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: stateful-nfs
  namespace: xiaojiang-test
provisioner: zjz                #这个要和nfs-client-provisioner的env环境变量中的PROVISIONER_NAME的value值对应。
reclaimPolicy: Retain               #指定回收策略为Retain（手动释放）
[root@master ~]# kubectl apply -f sc.yaml 
[root@master ~]# kubectl get StorageClass
NAME           PROVISIONER   AGE
stateful-nfs   zjz           7s

5）创建Pod

[root@master ~]# vim statefulset.yaml 
apiVersion: v1
kind: Service
metadata:
  name: headless-svc                    #从名称就可以是无头服务
  labels:
    app: headless-svc
spec:
  ports:
  - port: 80
    name: myweb
  selector:
    app: headless-pod
  clusterIP: None                        #不分配群集的IP地址，所以不具备负载均衡的能力
---
apiVersion: apps/v1
kind: StatefulSet                          #定义pod中运行的应用
metadata:
  name: statefulset-test
spec:
  serviceName: headless-svc
  replicas: 3
  selector:
    matchLabels:
      app: headless-pod
  template:
    metadata:
      labels:
        app: headless-pod
    spec:
      containers:
      - image: httpd
        name: myhttpd
        ports:
        - containerPort: 80
          name: httpd
        volumeMounts:
        - mountPath: /usr/local/apache2/htdocs
          name: test
  volumeClaimTemplates:                       #定义创建PVC使用的模板
  - metadata:
      name: test
      annotations:  #这是指定storageclass
        volume.beta.kubernetes.io/storage-class: stateful-nfs
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 100Mi
[root@master ~]# kubectl apply -f statefulset.yaml 
[root@master ~]# kubectl get pod  #这里需要等待一会儿
NAME                                      READY   STATUS    RESTARTS   AGE
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running   0          4m54s
statefulset-test-0                        1/1     Running   0          94s
statefulset-test-1                        1/1     Running   0          55s
statefulset-test-2                        1/1     Running   0          20s
[root@master ~]# kubectl get pv #查看pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                             STORAGECLASS   REASON   AGE
pvc-6c4d3c6f-6279-4ea6-ad8e-10d3098ea0eb   100Mi      RWO            Delete           Bound    default/test-statefulset-test-2   stateful-nfs            61s
pvc-d01c09ab-1399-49d9-bde6-812ad557f952   100Mi      RWO            Delete           Bound    default/test-statefulset-test-0   stateful-nfs            2m15s
pvc-e2257b8f-9deb-4398-85ed-b540a5880e08   100Mi      RWO            Delete           Bound    default/test-statefulset-test-1   stateful-nfs            96s
[root@master ~]# kubectl get pvc  #查看pvc
NAME                      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
test-statefulset-test-0   Bound    pvc-d01c09ab-1399-49d9-bde6-812ad557f952   100Mi      RWO            stateful-nfs   2m20s
test-statefulset-test-1   Bound    pvc-e2257b8f-9deb-4398-85ed-b540a5880e08   100Mi      RWO            stateful-nfs   101s
test-statefulset-test-2   Bound    pvc-6c4d3c6f-6279-4ea6-ad8e-10d3098ea0eb   100Mi      RWO            stateful-nfs   66s
[root@master ~]# ls /nfsdata/
default-test-statefulset-test-0-pvc-d01c09ab-1399-49d9-bde6-812ad557f952
default-test-statefulset-test-1-pvc-e2257b8f-9deb-4398-85ed-b540a5880e08
default-test-statefulset-test-2-pvc-6c4d3c6f-6279-4ea6-ad8e-10d3098ea0eb
#pod里写测试内容
[root@master ~]# echo "0000" > /nfsdata/default-test-statefulset-test-0-pvc-d01c09ab-1399-49d9-bde6-812ad557f952/index.html
[root@master ~]# echo "1111" > /nfsdata/default-test-statefulset-test-1-pvc-e2257b8f-9deb-4398-85ed-b540a5880e08/index.html
[root@master ~]# echo "2222" > /nfsdata/default-test-statefulset-test-2-pvc-6c4d3c6f-6279-4ea6-ad8e-10d3098ea0eb/index.html
#查看podip进行测试
[root@master ~]# kubectl get pod -o wide
NAME                                      READY   STATUS    RESTARTS   AGE     IP           NODE     NOMINATED NODE   READINESS GATES
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running   0          8m49s   10.244.1.2   node01              
statefulset-test-0                        1/1     Running   0          5m29s   10.244.2.2   node02              
statefulset-test-1                        1/1     Running   0          4m50s   10.244.1.3   node01              
statefulset-test-2                        1/1     Running   0          4m15s   10.244.2.3   node02              
#测试
[root@master ~]# curl 10.244.1.3
1111
[root@master ~]# curl 10.244.2.3
2222
[root@master ~]# curl 10.244.2.2
0000
[root@master ~]# curl -I 10.244.2.2
HTTP/1.1 200 OK
Date: Fri, 21 Aug 2020 03:45:16 GMT
Server: Apache/2.4.46 (Unix)
Last-Modified: Fri, 21 Aug 2020 03:33:50 GMT
ETag: "5-5ad5ae7c9eb7a"
Accept-Ranges: bytes
Content-Length: 5
Content-Type: text/html
#可以看出现在提供web页面的服务是Apache

#在pod里相应的目录下查看建立的测试内容
[root@master ~]# kubectl exec statefulset-test-0 cat /usr/local/apache2/htdocs/index.html
0000
[root@master ~]# kubectl exec statefulset-test-1 cat /usr/local/apache2/htdocs/index.html
1111
[root@master ~]# kubectl exec statefulset-test-2 cat /usr/local/apache2/htdocs/index.html
2222
#删除一个pod，测试数据是否会丢失
[root@master ~]# kubectl delete pod statefulset-test-2
pod "statefulset-test-2" deleted
#删除之后肯定会建立新的pod
[root@master ~]# kubectl get pod
NAME                                      READY   STATUS              RESTARTS   AGE
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running             0          15m
statefulset-test-0                        1/1     Running             0          12m
statefulset-test-1                        1/1     Running             0          11m
statefulset-test-2                        0/1     ContainerCreating   0          12s
#建立新的pod完成
[root@master ~]# kubectl get pod
NAME                                      READY   STATUS    RESTARTS   AGE
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running   0          15m
statefulset-test-0                        1/1     Running   0          12m
statefulset-test-1                        1/1     Running   0          11m
statefulset-test-2                        1/1     Running   0          18s
#再次查看数据
[root@master ~]# kubectl exec statefulset-test-2 cat /usr/local/apache2/htdocs/index.html
2222

6）对pod进行更新并扩容 （注释#的地方注意修改）

[root@master ~]# vim statefulset.yaml 
apiVersion: v1
kind: Service
metadata:
  name: headless-svc
  labels:
    app: headless-svc
spec:
  ports:
  - port: 80
    name: myweb
  selector:
    app: headless-pod
  clusterIP: None
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: statefulset-test
spec:
  updateStrategy:
    rollingUpdate:
      partition: 2                           #默认值为0（表示所有都会更新），值为2表示第三个pod进行更新
  serviceName: headless-svc
  replicas: 10
  selector:
    matchLabels:
      app: headless-pod
  template:
    metadata:
      labels:
        app: headless-pod
    spec:
      containers:
      - image: nginx                       #更换扩容时使用的镜像
        name: myhttpd
        ports:
        - containerPort: 80
          name: httpd
        volumeMounts:
        - mountPath: /usr/share/nginx/html/                 #更换容器中的主目录
          name: test
  volumeClaimTemplates:
  - metadata:
      name: test
      annotations:  #这是指定storageclass
        volume.beta.kubernetes.io/storage-class: stateful-nfs
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 100Mi
[root@master ~]# kubectl apply -f statefulset.yaml 
[root@master ~]# kubectl get pod -o wide   #需要等待一会儿
NAME                                      READY   STATUS        RESTARTS   AGE     IP           NODE     NOMINATED NODE   READINESS GATES
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running       0          31m     10.244.1.2   node01              
statefulset-test-0                        1/1     Running       0          28m     10.244.2.2   node02              
statefulset-test-1                        1/1     Running       0          28m     10.244.1.3   node01              
statefulset-test-2                        0/1     Terminating   0          16m     10.244.2.4   node02              
statefulset-test-3                        1/1     Running       0          2m34s   10.244.1.4   node01              
statefulset-test-4                        1/1     Running       0          2m10s   10.244.2.5   node02              
statefulset-test-5                        1/1     Running       0          102s    10.244.1.5   node01              
statefulset-test-6                        1/1     Running       0          83s     10.244.1.6   node01              
statefulset-test-7                        1/1     Running       0          63s     10.244.2.6   node02              
statefulset-test-8                        1/1     Running       0          42s     10.244.1.7   node01              
statefulset-test-9                        1/1     Running       0          23s     10.244.2.7   node02              
[root@master ~]# ls /nfsdata/
default-test-statefulset-test-0-pvc-d01c09ab-1399-49d9-bde6-812ad557f952
default-test-statefulset-test-1-pvc-e2257b8f-9deb-4398-85ed-b540a5880e08
default-test-statefulset-test-2-pvc-6c4d3c6f-6279-4ea6-ad8e-10d3098ea0eb
default-test-statefulset-test-3-pvc-95724e2b-e30a-4c8c-a56d-9b9aa46d286c
default-test-statefulset-test-4-pvc-8d93522b-ccf6-492e-9adf-93a933214398
default-test-statefulset-test-5-pvc-cfbe5307-e756-487e-b03f-2edc62a86884
default-test-statefulset-test-6-pvc-e965f491-e04e-4488-9ee9-8069b2a224f1
default-test-statefulset-test-7-pvc-b9ca6c86-63f1-4b3a-9461-d1e844029d97
default-test-statefulset-test-8-pvc-7ff2c99a-34fe-4de3-bb70-d842d68b74d7
default-test-statefulset-test-9-pvc-3f01625d-28ba-4655-a3c8-54a4b8a89a81
[root@master ~]# ls /nfsdata/ | wc -l
10
[root@master ~]# kubectl get pod -o wide
NAME                                      READY   STATUS    RESTARTS   AGE     IP           NODE     NOMINATED NODE   READINESS GATES
nfs-client-provisioner-74cf5dd55f-7fvr5   1/1     Running   0          33m     10.244.1.2   node01              
statefulset-test-0                        1/1     Running   0          29m     10.244.2.2   node02              
statefulset-test-1                        1/1     Running   0          29m     10.244.1.3   node01              
statefulset-test-2                        1/1     Running   0          62s     10.244.2.8   node02              
statefulset-test-3                        1/1     Running   0          3m45s   10.244.1.4   node01              
statefulset-test-4                        1/1     Running   0          3m21s   10.244.2.5   node02              
statefulset-test-5                        1/1     Running   0          2m53s   10.244.1.5   node01              
statefulset-test-6                        1/1     Running   0          2m34s   10.244.1.6   node01              
statefulset-test-7                        1/1     Running   0          2m14s   10.244.2.6   node02              
statefulset-test-8                        1/1     Running   0          113s    10.244.1.7   node01              
statefulset-test-9                        1/1     Running   0          94s     10.244.2.7   node02              
#由于配置文件中写的是 partition: 2  ，（2表示第三个pod进行更新），所以statefulset-test-0 statefulset-test-1 statefulset-test-2是apache，后面的是nginx
[root@master ~]# curl -I 10.244.2.2
HTTP/1.1 200 OK
Date: Fri, 21 Aug 2020 04:02:20 GMT
Server: Apache/2.4.46 (Unix)
Last-Modified: Fri, 21 Aug 2020 03:33:50 GMT
ETag: "5-5ad5ae7c9eb7a"
Accept-Ranges: bytes
Content-Length: 5
Content-Type: text/html

[root@master ~]# curl -I 10.244.1.4
HTTP/1.1 403 Forbidden
Server: nginx/1.19.2
Date: Fri, 21 Aug 2020 04:02:37 GMT
Content-Type: text/html
Content-Length: 153
Connection: keep-alive

由此可以看出在在扩容、缩容过程中，pod的生成或删除操作也是有顺序；并不会更改pod，这就是StatefulSet的特点！