k8s实践之mysql集群搭建

本篇文章我们实践用k8s搭建一个mysql集群，文章参考自极客时间张磊老师的课程：深入剖析 Kubernetes。

1.local pv的搭建

假设我们的k8s集群有hostname为node-1，node-2，node-3的三台主机。首先，在宿主机上创建一个挂载点，比如/mnt/disks，然后用 RAM Disk 来模拟本地磁盘，在node-1上执行：

$ mkdir /mnt/disks
$ mkdir /mnt/disks/vol1
$ mount -t tmpfs vol1 /mnt/disks/vol1

在其余两台主机执行时，将路径替换为vol2、vol3以作区分。

然后为这些本地磁盘定义对应的 PV，pv-1.yaml、pv-2.yaml、pv-3.yaml，注释的地方为需要替换的地方：

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-1 # pv-2 pv-3
spec:
  capacity:
    storage: 1Gi
  volumeMode: Filesystem
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Delete
  storageClassName: local-storage
  local:
    path: /mnt/disks/vol1 # vol2 vol3
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - node-1 # node-2 node-3

在master节点上执行：（后面的yaml文件都需要这样操作，不再赘述）

kubectl apply -f pv-1.yaml pv-2.yaml pv-3.yaml

接着创建一个 StorageClass 来描述这个 PV，如下所示：

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

2.mysql配置文件ConfigMap

Master 节点和 Slave 节点需要有不同的配置文件：我们只需要给主从节点分别准备两份不同的 MySQL 配置文件，然后根据 Pod 的序号（Index）挂载进去即可。这样的配置文件信息，应该保存在 ConfigMap 里供 Pod 使用。

apiVersion: v1
kind: ConfigMap
metadata:
  name: mysql
  labels:
    app: mysql
data:
  master.cnf: |
    # 主节点MySQL的配置文件
    [mysqld]
    log-bin
  slave.cnf: |
    # 从节点MySQL的配置文件
    [mysqld]
    super-read-only

3.Service的定义

这两个 Service 都代理了所有携带 app=mysql 标签的 Pod，也就是所有的 MySQL Pod。端口映射都是用 Service 的 3306 端口对应 Pod 的 3306 端口。

所有用户的读请求，都必须访问第二个 Service 被自动分配的 DNS 记录，即mysql-read。这样，读请求就可以被转发到任意一个 MySQL 的主节点或者从节点上。而所有用户的写请求，则必须直接以 DNS 记录的方式访问到 MySQL 的主节点，即mysql-0.mysql这条 DNS 记录。

apiVersion: v1
kind: Service
metadata:
  name: mysql
  labels:
    app: mysql
spec:
  ports:
  - name: mysql
    port: 3306
  clusterIP: None
  selector:
    app: mysql
---
apiVersion: v1
kind: Service
metadata:
  name: mysql-read
  labels:
    app: mysql
spec:
  ports:
  - name: mysql
    port: 3306
  selector:
    app: mysql

4.StatefulSet的定义

init-mysql从 ConfigMap 中，获取 MySQL 的 Pod 对应的配置文件，根据节点的角色是 Master 还是 Slave 节点，为 Pod 分配对应的配置文件。此外，MySQL 还要求集群里的每个节点都有一个唯一的 ID 文件，名叫 server-id.cnf。

clone-mysql在 Slave Pod 启动前，从 Master 或者其他 Slave Pod 里拷贝数据库数据到自己的目录下。

xtrabackup在 Slave 节点的 MySQL 容器第一次启动之前，执行初始化 SQL。

mysql是集群里Mysql容器的定义。

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
          # 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 [[ $ordinal -eq 0 ]]; then
            cp /mnt/config-map/primary.cnf /mnt/conf.d/
          else
            cp /mnt/config-map/replica.cnf /mnt/conf.d/
          fi          
        volumeMounts:
        - name: conf
          mountPath: /mnt/conf.d
        - name: config-map
          mountPath: /mnt/config-map
      - name: clone-mysql
        image: gcr.io/google-samples/xtrabackup:1.0
        command:
        - bash
        - "-c"
        - |
          set -ex
          # Skip the clone if data already exists.
          [[ -d /var/lib/mysql/mysql ]] && exit 0
          # Skip the clone on primary (ordinal index 0).
          [[ `hostname` =~ -([0-9]+)$ ]] || 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
        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: gcr.io/google-samples/xtrabackup:1.0
        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$(<xtrabackup_slave_info)" != "x" ]]; then
            # XtraBackup already generated a partial "CHANGE MASTER TO" query
            # because we're cloning from an existing replica. (Need to remove the tailing semicolon!)
            cat xtrabackup_slave_info | sed -E 's/;$//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 primary. 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:
      accessModes: ["ReadWriteOnce"]
      storageClassName: local-storage
      resources:
        requests:
          storage: 1Gi

5.集群操作

查看集群状态：

$ kubectl get pod -l app=mysql
NAME      READY     STATUS    RESTARTS   AGE
mysql-0   2/2       Running   0          2m
mysql-1   2/2       Running   0          1m
mysql-2   2/2       Running   0          1m

向这个 MySQL 集群发起写请求：

$ 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

向这个 MySQL 集群发起读请求：

$ kubectl run mysql-client --image=mysql:5.7 -i -t --rm --restart=Never --\
 mysql -h mysql-read -e "SELECT * FROM test.messages"
Waiting for pod default/mysql-client to be running, status is Pending, pod ready: false
+---------+
| message |
+---------+
| hello   |
+---------+
pod "mysql-client" deleted

集群的伸缩：

$ kubectl scale statefulset mysql  --replicas=2