StatefulSet应用案例-MySQL主从

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环境：

名称 版本 其他
K8S 1.20+ 至少三个节点
MySql 5.7+ 一主二从
NFS服务器 系统默认版本 192.168.8.201

要求：

展示如何使用 StatefulSet 控制器运行一个有状态的应用程序。此例是多副本的 MySQL 数据库。 示例应用的拓扑结构有一个主服务器和多个副本，使用异步的基于行（Row-Based） 的数据复制。

  • 搭建一个“主从复制”（Maser-Slave Replication）的 MySQL 集群
  • 存在一个主节点【master】，有多个从节点【slave】
  • 从节点可以水平拓展
  • 所有的写操作，只能在主节点上执行
  • 读操作可以在所有节点上执行

一、部署NFS服务器

# 服务器安装nfs服务，提供nfs存储功能
# 1、centos7安装nfs-utils
yum install nfs-utils 

# 或者 (ubuntu)  
# apt-get install nfs-kernel-server 

# 2、启动服务
systemctl enable nfs-server
systemctl start nfs-server

# 3、创建共享目录完成共享配置
# 创建共享目录
mkdir -p /data/nfs-mysql-{1..3}

# 4、编辑共享配置
vim /etc/exports
#语法格式：共享文件路径    客户机地址（权限）
#这里的客户机地址可以是IP,网段,域名,也可以是任意*
/data/nfs-mysql-1 *(rw,no_root_squash,no_all_squash,sync)
/data/nfs-mysql-2 *(rw,no_root_squash,no_all_squash,sync)
/data/nfs-mysql-3 *(rw,no_root_squash,no_all_squash,sync)

# 服务自检命令
exportfs -arv

# 5、重启服务
systemctl restart nfs-server

# 6、本机查看nfs 共享目录
# showmount -e 服务器IP地址
# (如果提示命令不存在，则需要yum install showmount)
showmount -e 127.0.0.1

# 7、客户端模拟挂载[所有k8s的节点都需要安装客户端]
# centos
yum install nfs-utils
# 或者（ubuntu）
# apt-get install nfs-common

# 挂载测试
mkdir /test
mount -t nfs 192.168.8.201:/data/nfs-mysql-1  /test
# 取消挂载
umount /test

二、配置PV

[root@k8s-master-1 ~]# mkdir /root/k8s-mysql
[root@k8s-master-1 ~]# cd /root/k8s-mysql
[root@k8s-master-1 k8s-mysql]# vim mysql-pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv001
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: managed-nfs-storage
  nfs:
    path: /data/nfs-mysql-1
    server: 192.168.8.201
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv002
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: managed-nfs-storage
  nfs:
    path: /data/nfs-mysql-2
    server: 192.168.8.201
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv003
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: managed-nfs-storage
  nfs:
    path: /data/nfs-mysql-3
    server: 192.168.8.201
  • 创建PV
kubectl apply -f mysql-pv.yaml
kubectl get pv

image-20240519112641494

三、编写mysql 相关yaml文件

MySQL 示例部署包含一个 ConfigMap、两个 Service 与一个 StatefulSet。

ConfigMap:

[root@k8s-master-1 k8s-mysql]# vim mysql-configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: mysql
  labels:
    app: mysql
data:
  master.cnf: |
    # Apply this config only on the master.
    [mysqld]
    log-bin
  slave.cnf: |
    # Apply this config only on slaves.
    [mysqld]
    super-read-only

说明：在这里，我们定义了 master.cnf 和 slave.cnf 两个 MySQL 的配置文件

  • master.cnf 开启了log-bin，可以使用二进制日志文件的方式进行主从复制.
  • slave.cnf 开启了 super-read-only ，表示从节点只接受主节点的数据同步的所有写的操作，拒绝其他的写入操作，对于用户来说就是只读的
  • master.cnf 和 slave.cnf 已配置文件的形式挂载到容器的目录中

Service:

[root@k8s-master-1 k8s-mysql]# vim mysql-services.yaml
# Headless service for stable DNS entries of StatefulSet members.
apiVersion: v1
kind: Service
metadata:
  name: mysql
  labels:
    app: mysql
spec:
  ports:
  - name: mysql
    port: 3306
  clusterIP: None
  selector:
    app: mysql
---
# Client service for connecting to any MySQL instance for reads.
# For writes, you must instead connect to the master: mysql-0.mysql.
apiVersion: v1
kind: Service
metadata:
  name: mysql-read
  labels:
    app: mysql
spec:
  ports:
  - name: mysql
    port: 3306
  selector:
    app: mysql

说明：

  • clusterIP: None，使用无头服务 Headless Service（相比普通Service只是将spec.clusterIP定义为None，也就是没有clusterIP，直接使用endport 来通信）来维护Pod网络身份，会为每个Pod分配一个数字编号并且按照编号顺序部署。还需要在StatefulSet添加serviceName: “mysql”字段指定StatefulSet控制器
  • 另外statefulset控制器网络标识，体现在主机名和Pod A记录：
    • 主机名：<statefulset名称>-<编号>例如: mysql-0
    • Pod DNS A记录：<statefulset名称-编号>.<service-name> .<namespace>.svc.cluster.local （POD 之间通过DNS A 记录互相通信）例如:mysql-0.mysql.default.svc.cluster.local

StatefulSet:

[root@k8s-master-1 k8s-mysql]# vim mysql-statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
  serviceName: mysql
  replicas: 3
  template:
    metadata:
      labels:
        app: mysql
    spec:
      initContainers:
      - name: init-mysql
        image: mysql:5.7
        imagePullPolicy: IfNotPresent
        command:
        - bash
        - "-c"
        - |
          set -ex
          # Generate mysql server-id from pod ordinal index.
          [[ `hostname` =~ -([0-9]+)$ ]] || exit 1
          ordinal=${BASH_REMATCH[1]}
          echo [mysqld] > /mnt/conf.d/server-id.cnf
          # Add an offset to avoid reserved server-id=0 value.
          echo server-id=$((100 + $ordinal)) >> /mnt/conf.d/server-id.cnf
          # Copy appropriate conf.d files from config-map to emptyDir.
          if [[ $ordinal -eq 0 ]]; then
            cp /mnt/config-map/master.cnf /mnt/conf.d/
          else
            cp /mnt/config-map/slave.cnf /mnt/conf.d/
          fi          
        volumeMounts:
        - name: conf
          mountPath: /mnt/conf.d
        - name: config-map
          mountPath: /mnt/config-map
      - name: clone-mysql
        image: fxkjnj/xtrabackup:1.0
        imagePullPolicy: IfNotPresent
        command:
        - bash
        - "-c"
        - |
          set -ex
          # Skip the clone if data already exists.
          [[ -d /var/lib/mysql/mysql ]] && exit 0
          # Skip the clone on master (ordinal index 0).
          [[ `hostname` =~ -([0-9]+)$ ]] || exit 1
          ordinal=${BASH_REMATCH[1]}
          [[ $ordinal -eq 0 ]] && exit 0
          # Clone data from previous peer.
          ncat --recv-only mysql-$(($ordinal-1)).mysql 3307 | xbstream -x -C /var/lib/mysql
          # Prepare the backup.
          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
        imagePullPolicy: IfNotPresent
        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: 1Gi
        livenessProbe:
          exec:
            command: ["mysqladmin", "ping"]
          initialDelaySeconds: 30
          periodSeconds: 10
          timeoutSeconds: 5
        readinessProbe:
          exec:
            # Check we can execute queries over TCP (skip-networking is off).
            command: ["mysql", "-h", "127.0.0.1", "-e", "SELECT 1"]
          initialDelaySeconds: 5
          periodSeconds: 2
          timeoutSeconds: 1
      - name: xtrabackup
        image: fxkjnj/xtrabackup:1.0
        imagePullPolicy: IfNotPresent
        ports:
        - name: xtrabackup
          containerPort: 3307
        command:
        - bash
        - "-c"
        - |
          set -ex
          cd /var/lib/mysql

          # Determine binlog position of cloned data, if any.
          if [[ -f xtrabackup_slave_info && "x$(<xtrabackup_slave_info)" != "x" ]]; then
            # XtraBackup already generated a partial "CHANGE MASTER TO" query
            # because we're cloning from an existing slave. (Need to remove the tailing semicolon!)
            cat xtrabackup_slave_info | sed -E 's/;$//g' > change_master_to.sql.in
            # Ignore xtrabackup_binlog_info in this case (it's useless).
            rm -f xtrabackup_slave_info xtrabackup_binlog_info
          elif [[ -f xtrabackup_binlog_info ]]; then
            # We're cloning directly from master. Parse binlog position.
            [[ `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
          # Check if we need to complete a clone by starting replication.
          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
            # In case of container restart, attempt this at-most-once.
            mv change_master_to.sql.in change_master_to.sql.orig
          fi
          # Start a server to send backups when requested by peers.
          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:
      storageClassName: "managed-nfs-storage"
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 0.5Gi

说明：

  • 使用xtrbackup 工具进行容器初始化数据的备份
  • 使用linux 自带的ncat 工具进行容器初始化数据的拷贝
  • 使用mysql的binlog 主从复制 来保证主从之间的数据一致
  • 利用pod的主机名的序号来判断当前节点为主节点还是从节点
  • 对于节点拷贝不同的配置文件到指定位置
  • 使用mysqladmin的ping 作为数据库的健康检测方式
  • 使用nfs存储的 PV 动态供给（StorageClass），持久化mysql的数据文件

四、部署并测试

[root@k8s-master-1 k8s-mysql]#  ll
total 28
drwxr-xr-x 2 root root 4096 May 19 11:25 ./
drwxr-xr-x 3 root root 4096 May 19 10:51 ../
-rw-r--r-- 1 root root  259 May 19 11:08 mysql-configmap.yaml
-rw-r--r-- 1 root root  839 May 19 11:25 mysql-pv.yaml
-rw-r--r-- 1 root root  463 May 19 11:09 mysql-services.yaml
-rw-r--r-- 1 root root 5864 May 19 11:10 mysql-statefulset.yaml

[root@k8s-master-1 k8s-mysql]# kubectl apply -f .
configmap/mysql create
service/mysql create
service/mysql-read create
statefulset.apps/mysql create

#动态追踪查看Pod的状态：
[root@k8s-master-1 k8s-mysql]#  kubectl get pods -l app=mysql --watch
NAME      READY   STATUS    RESTARTS   AGE
mysql-0   2/2     Running   0          3h12m
mysql-1   2/2     Running   0          3h11m
mysql-2   2/2     Running   0          3h10m

可以看到，StatefulSet 启动成功后，将会有三个 Pod 运行。

image-20240519113008559

接下来，我们可以尝试向这个 MySQL 集群发起请求，执行一些 SQL 操作来验证它是否正常：

kubectl run mysql-client --image=mysql:5.7 -i --rm --restart=Never --\
 mysql -h mysql-0.mysql <<EOF
CREATE DATABASE test;
CREATE TABLE test.messages (message VARCHAR(250));
INSERT INTO test.messages VALUES ('hello');
EOF

如上所示，我们通过启动一个容器，使用 MySQL client 执行了创建数据库和表、以及插入数据的操作。需要注意的是，我们连接的 MySQL 的地址必须是 mysql-0.mysql（即：Master 节点的 DNS A 记录, 因为POD 之间通过DNS A 记录互相通信）只有 Master 节点才能处理写操作。

而通过连接 mysql-read 这个 Service，我们就可以用 SQL 进行读操作，如下所示：

kubectl run mysql-client --image=mysql:5.7 -i -t --rm --restart=Never --\
  mysql -h mysql-read -e "SELECT * FROM test.messages"

#你应该获得如下输出：
Waiting for pod default/mysql-client to be running, status is Pending, pod ready: false
+---------+
| message |
+---------+
| hello   |
+---------+
pod "mysql-client" deleted

或者：

kubectl run -it --rm --image=mysql:5.7 --restart=Never mysql-client -- mysql -h mysql-read
If you don't see a command prompt, try pressing enter.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 305
Server version: 5.7.36 MySQL Community Server (GPL)

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+------------------------+
| Database               |
+------------------------+
| information_schema     |
| mysql                  |
| performance_schema     |
| sys                    |
| test                   |
| xtrabackup_backupfiles |
+------------------------+
6 rows in set (0.02 sec)

mysql> use test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| messages       |
+----------------+
1 row in set (0.00 sec)

mysql> select * from messages;
+---------+
| message |
+---------+
| hello   |
+---------+
1 row in set (0.00 sec)

mysql> exit
Bye
pod "mysql-client" deleted

作业

参考本节案例，通过查找资料在K8S中实现Redis哨兵模式。