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一、StatefulSet简介

• StatefulSet将应用状态抽象成了两种情况：
  拓扑状态：应用实例必须按照某种顺序启动。新创建的Pod必须和原来Pod的网络标识一样
  存储状态：应用的多个实例分别绑定了不同存储数据。

• StatefulSet给所有的Pod进行了编号，编号规则是：$(statefulset名称)-$(序号)，从0开始。

• StatefulSet还会为每一个Pod分配并创建一个同样编号的PVC。这样，kubernetes就可以通过Persistent Volume机制为这个PVC绑定对应的PV，从而保证每一个Pod都拥有一个独立的Volume。

• Pod被删除后重建，重建Pod的网络标识也不会改变,Pod的拓扑状态按照Pod的“名字+编号”的方式固定下来,并且为每个Pod提供了一个固定且唯一的访问入口,即Pod对应的DNS记录。

二、statefulset控制器：示例

1.代码演示

[root@k8s2 statefulset]# vim headless.yaml            ##目录位置任意
apiVersion: v1
kind: Service
metadata:
 name: nginx-svc
 labels:
  app: nginx
spec:
 ports:
 - port: 80
   name: web
 clusterIP: None
 selector:
  app: nginx
[root@k8s2 statefulset]# kubectl apply -f headless.yaml
[root@k8s2 statefulset]# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   6d23h
nginx-svc    ClusterIP   None         <none>        80/TCP    2s

[root@k8s2 statefulset]# vim statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet
metadata:
 name: web
spec:
 serviceName: "nginx-svc"
 replicas: 3
 selector:
  matchLabels:
   app: nginx
 template:
  metadata:
   labels:
    app: nginx
  spec:
   containers:
   - name: nginx
     image: nginx
     volumeMounts:
       - name: www
         mountPath: /usr/share/nginx/html
 volumeClaimTemplates:
  - metadata:
     name: www
    spec:
     storageClassName: nfs-client
     accessModes:
     - ReadWriteOnce
     resources:
      requests:
       storage: 1Gi

[root@k8s2 statefulset]# kubectl apply -f statefulset.yaml
[root@k8s2 statefulset]# kubectl get pod
NAME    READY   STATUS    RESTARTS   AGE
web-0   1/1     Running   0          75s
web-1   1/1     Running   0          5s
web-2   1/1     Running   0          4s

在nfs输出目录创建测试页

[root@k8s2 statefulset]# kubectl run demo --image busyboxplus -it
/ # curl  web-0.nginx-svc
web-0
/ # curl  web-1.nginx-svc
web-1
/ # curl  web-2.nginx-svc
web-2

statefulset有序回收
kubectl scale statefulsets web --replicas=0
[root@k8s2 statefulset]# kubectl delete -f statefulset.yaml
[root@k8s2 mysql]# kubectl delete pvc --all

2.补充

• kubectl 弹缩
  首先,想要弹缩的StatefulSet. 需先清楚是否能弹缩该应用.
  $ kubectl get statefulsets
  改变StatefulSet副本数量:
  $ kubectl scale statefulsets --replicas=

• 如果StatefulSet开始由 kubectl apply 或 kubectl create --save-config 创建,更新StatefulSet manifests中的 .spec.replicas, 然后执行命令 kubectl apply:
  $ kubectl apply -f

• 也可以通过命令 kubectl edit 编辑该字段:
  $ kubectl edit statefulsets

• 使用 kubectl patch:
  $ kubectl patch statefulsets -p ‘{“spec”:{“replicas”:}}’

三、statefulset部署mysql主从部署

官网：https://v1-25.docs.kubernetes.io/zh-cn/docs/tasks/run-application/run-replicated-stateful-application/
首先上传镜像，确保仓库中有以下两个镜像

[root@k8s2 mysql]# vim configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: mysql
  labels:
    app: mysql
    app.kubernetes.io/name: mysql
data:
  primary.cnf: |
    [mysqld]
    log-bin
  replica.cnf: |
    [mysqld]
    super-read-only
[root@k8s2 mysql]# kubectl apply -f configmap.yaml

[root@k8s2 mysql]# vim svc.yaml
apiVersion: v1
kind: Service
metadata:
  name: mysql
  labels:
    app: mysql
    app.kubernetes.io/name: mysql
spec:
  ports:
  - name: mysql
    port: 3306
  clusterIP: None
  selector:
    app: mysql
---
apiVersion: v1
kind: Service
metadata:
  name: mysql-read
  labels:
    app: mysql
    app.kubernetes.io/name: mysql
    readonly: "true"
spec:
  ports:
  - name: mysql
    port: 3306
  selector:
    app: mysql
[root@k8s2 mysql]# kubectl apply -f svc.yaml
[root@k8s2 mysql]# kubectl get svc
NAME         TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)    AGE
kubernetes   ClusterIP   10.96.0.1      <none>        443/TCP    7d
mysql        ClusterIP   None           <none>        3306/TCP   23m
mysql-read   ClusterIP   10.98.32.113   <none>        3306/TCP   23m

[root@k8s2 mysql]# vim statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
      app.kubernetes.io/name: mysql
  serviceName: mysql
  replicas: 3
  template:
    metadata:
      labels:
        app: mysql
        app.kubernetes.io/name: mysql
    spec:
      initContainers:
      - name: init-mysql
        image: mysql:5.7
        command:
        - bash
        - "-c"
        - |
          set -ex
          # 基于 Pod 序号生成 MySQL 服务器的 ID。
          [[ $HOSTNAME =~ -([0-9]+)$ ]] || exit 1
          ordinal=${BASH_REMATCH[1]}
          echo [mysqld] > /mnt/conf.d/server-id.cnf
          # 添加偏移量以避免使用 server-id=0 这一保留值。
          echo server-id=$((100 + $ordinal)) >> /mnt/conf.d/server-id.cnf
          # 将合适的 conf.d 文件从 config-map 复制到 emptyDir。
          if [[ $ordinal -eq 0 ]]; then
            cp /mnt/config-map/primary.cnf /mnt/conf.d/
          else
            cp /mnt/config-map/replica.cnf /mnt/conf.d/
          fi
        volumeMounts:
        - name: conf
          mountPath: /mnt/conf.d
        - name: config-map
          mountPath: /mnt/config-map
      - name: clone-mysql
        image: xtrabackup:1.0
        command:
        - bash
        - "-c"
        - |
          set -ex
          # 如果已有数据，则跳过克隆。
          [[ -d /var/lib/mysql/mysql ]] && exit 0
          # 跳过主实例（序号索引 0）的克隆。
          [[ `hostname` =~ -([0-9]+)$ ]] || exit 1
          ordinal=${BASH_REMATCH[1]}
          [[ $ordinal -eq 0 ]] && exit 0
          # 从原来的对等节点克隆数据。
          ncat --recv-only mysql-$(($ordinal-1)).mysql 3307 | xbstream -x -C /var/lib/mysql
          # 准备备份。
          xtrabackup --prepare --target-dir=/var/lib/mysql
        volumeMounts:
        - name: data
          mountPath: /var/lib/mysql
          subPath: mysql
        - name: conf
          mountPath: /etc/mysql/conf.d
      containers:
      - name: mysql
        image: mysql:5.7
        env:
        - name: MYSQL_ALLOW_EMPTY_PASSWORD
          value: "1"
        ports:
        - name: mysql
          containerPort: 3306
        volumeMounts:
        - name: data
          mountPath: /var/lib/mysql
          subPath: mysql
        - name: conf
          mountPath: /etc/mysql/conf.d
        resources:
          requests:
            cpu: 500m
            memory: 512Mi
        livenessProbe:
          exec:
            command: ["mysqladmin", "ping"]
          initialDelaySeconds: 30
          periodSeconds: 10
          timeoutSeconds: 5
        readinessProbe:
          exec:
            # 检查我们是否可以通过 TCP 执行查询（skip-networking 是关闭的）。
            command: ["mysql", "-h", "127.0.0.1", "-e", "SELECT 1"]
          initialDelaySeconds: 5
          periodSeconds: 2
          timeoutSeconds: 1
      - name: xtrabackup
        image: xtrabackup:1.0
        ports:
        - name: xtrabackup
          containerPort: 3307
        command:
        - bash
        - "-c"
        - |
          set -ex
          cd /var/lib/mysql

          # 确定克隆数据的 binlog 位置（如果有的话）。
          if [[ -f xtrabackup_slave_info && "x$(<xtrabackup_slave_info)" != "x" ]]; then
            # XtraBackup 已经生成了部分的 “CHANGE MASTER TO” 查询
            # 因为我们从一个现有副本进行克隆。(需要删除末尾的分号!)
            cat xtrabackup_slave_info | sed -E 's/;$//g' > change_master_to.sql.in
            # 在这里要忽略 xtrabackup_binlog_info （它是没用的）。
            rm -f xtrabackup_slave_info xtrabackup_binlog_info
          elif [[ -f xtrabackup_binlog_info ]]; then
            # 我们直接从主实例进行克隆。解析 binlog 位置。
            [[ `cat xtrabackup_binlog_info` =~ ^(.*?)[[:space:]]+(.*?)$ ]] || exit 1
            rm -f xtrabackup_binlog_info xtrabackup_slave_info
            echo "CHANGE MASTER TO MASTER_LOG_FILE='${BASH_REMATCH[1]}',\
                  MASTER_LOG_POS=${BASH_REMATCH[2]}" > change_master_to.sql.in
          fi

          # 检查我们是否需要通过启动复制来完成克隆。
          if [[ -f change_master_to.sql.in ]]; then
            echo "Waiting for mysqld to be ready (accepting connections)"
            until mysql -h 127.0.0.1 -e "SELECT 1"; do sleep 1; done

            echo "Initializing replication from clone position"
            mysql -h 127.0.0.1 \
                  -e "$(<change_master_to.sql.in), \
                          MASTER_HOST='mysql-0.mysql', \
                          MASTER_USER='root', \
                          MASTER_PASSWORD='', \
                          MASTER_CONNECT_RETRY=10; \
                        START SLAVE;" || exit 1
            # 如果容器重新启动，最多尝试一次。
            mv change_master_to.sql.in change_master_to.sql.orig
          fi

          # 当对等点请求时，启动服务器发送备份。
          exec ncat --listen --keep-open --send-only --max-conns=1 3307 -c \
            "xtrabackup --backup --slave-info --stream=xbstream --host=127.0.0.1 --user=root"
        volumeMounts:
        - name: data
          mountPath: /var/lib/mysql
          subPath: mysql
        - name: conf
          mountPath: /etc/mysql/conf.d
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
      volumes:
      - name: conf
        emptyDir: {}
      - name: config-map
        configMap:
          name: mysql
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 10Gi

[root@k8s2 mysql]# kubectl apply -f statefulset.yaml

[root@k8s2 mysql]# kubectl get pod
NAME      READY   STATUS    RESTARTS   AGE
mysql-0   2/2     Running   0          13m
mysql-1   2/2     Running   0          6m51s
mysql-2   2/2     Running   0          4m3s

连接测试
[root@k8s2 mysql]# kubectl  run demo --image mysql:5.7 -it -- bash
If you don't see a command prompt, try pressing enter.
bash-4.2# mysql -h mysql-0.mysql

mysql> show databases;
...

回收
[root@k8s2 mysql]# kubectl delete -f statefulset.yaml
[root@k8s2 mysql]# kubectl delete pvc --all

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