K8S与Ceph RBD集成-多主与主从数据库示例

参考文章：

https://ieevee.com/tech/2018/05/16/k8s-rbd.html
https://zhangchenchen.github.io/2017/11/17/kubernetes-integrate-with-ceph/
https://docs.openshift.com/container-platform/3.5/install_config/storage_examples/ceph_rbd_dynamic_example.html
https://jimmysong.io/kubernetes-handbook/practice/using-ceph-for-persistent-storage.html

感谢以上作者提供的技术参考，这里我加以整理，分别实现了多主数据库集群和主从数据库结合Ceph RDB的实现方式。以下配置只为测试使用，不能做为生产配置。

K8S中存储的分类

在K8S的持久化存储中主要有以下几种分类：

• volume: 就是直接挂载在pod上的组件，k8s中所有的其他存储组件都是通过volume来跟pod直接联系的。volume有个type属性，type决定了挂载的存储是什么，常见的比如：emptyDir，hostPath，nfs，rbd，以及下文要说的persistentVolumeClaim等。跟docker里面的volume概念不同的是，docker里的volume的生命周期是跟docker紧紧绑在一起的。这里根据type的不同，生命周期也不同，比如emptyDir类型的就是跟docker一样，pod挂掉，对应的volume也就消失了，而其他类型的都是永久存储。详细介绍可以参考Volumes

• Persistent Volumes：顾名思义，这个组件就是用来支持永久存储的，Persistent Volumes组件会抽象后端存储的提供者（也就是上文中volume中的type）和消费者（即具体哪个pod使用）。该组件提供了PersistentVolume和PersistentVolumeClaim两个概念来抽象上述两者。一个PersistentVolume（简称PV）就是后端存储提供的一块存储空间，具体到ceph rbd中就是一个image，一个PersistentVolumeClaim（简称PVC）可以看做是用户对PV的请求，PVC会跟某个PV绑定，然后某个具体pod会在volume 中挂载PVC,就挂载了对应的PV。

• Dynamic Volume Provisioning: 动态volume发现，比如上面的Persistent Volumes,我们必须先要创建一个存储块，比如一个ceph中的image，然后将该image绑定PV，才能使用。这种静态的绑定模式太僵硬，每次申请存储都要向存储提供者索要一份存储快。Dynamic Volume Provisioning就是解决这个问题的。它引入了StorageClass这个概念，StorageClass抽象了存储提供者，只需在PVC中指定StorageClass，然后说明要多大的存储就可以了，存储提供者会根据需求动态创建所需存储快。甚至于，我们可以指定一个默认StorageClass，这样，只需创建PVC就可以了。

配置初始化环境

• 已经有一个k8s集群
• 已经有一个Ceph 集群

所有节点安装ceph-common

添加ceph的yum源：

[Ceph]name=Ceph packages for $basearchbaseurl=https://mirrors.aliyun.com/ceph/rpm-mimic/el7/$basearchenabled=1gpgcheck=1type=rpm-mdgpgkey=https://download.ceph.com/keys/release.asc[Ceph-noarch]name=Ceph noarch packagesbaseurl=https://mirrors.aliyun.com/ceph/rpm-mimic/el7/noarchenabled=1gpgcheck=1type=rpm-mdgpgkey=https://download.ceph.com/keys/release.asc[ceph-source]name=Ceph source packagesbaseurl=https://mirrors.aliyun.com/ceph/rpm-mimic/el7/SRPMSenabled=1gpgcheck=1type=rpm-mdgpgkey=https://download.ceph.com/keys/release.asc

安装ceph-common：

yum install ceph-common -y

如果安装过程出现依赖报错，可以通过如下方式解决：

yum install -y yum-utils && \yum-config-manager --add-repo https://dl.fedoraproject.org/pub/epel/7/x86_64/ && \yum install --nogpgcheck -y epel-release && \rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7 && \rm -f /etc/yum.repos.d/dl.fedoraproject.org*yum -y install ceph-common

配置ceph配置文件

将ceph配置文件拷贝到各个k8s的node节点

[root@ceph-1 ~]# scp /etc/ceph k8s-node:/etc/

测试volume

通过使用一个简单的volume,测试集群环境是否正常，在实际的应用中，需要永久保存的数据不能使用volume的方式。

在Ceph集群中创建images

创建新的镜像时，需要禁用某些不支持的属性：

 rbd create foobar -s 1024 -p k8s rbd feature disable k8s/foobar object-map fast-diff deep-flatten

查看镜像信息：

# rbd info k8s/foobarrbd image 'foobar':    size 1 GiB in 256 objects    order 22 (4 MiB objects)    id: ad9b6b8b4567    block_name_prefix: rbd_data.ad9b6b8b4567    format: 2    features: layering, exclusive-lock    op_features:     flags:     create_timestamp: Tue Apr 23 17:37:39 2019

使用POD直接挂载volume

这里指定了ceph的 admin.keyring文件作为认证密钥：

# cat test.yaml apiVersion: v1kind: Podmetadata:  name: rbdspec:  containers:    - image: nginx      name: rbd-rw      volumeMounts:      - name: rbdpd        mountPath: /mnt  volumes:    - name: rbdpd      rbd:        monitors:        - '192.168.20.41:6789'        pool: k8s        image: foobar        fsType: xfs        readOnly: false        user: admin        keyring: /etc/ceph/ceph.client.admin.keyring

使用PV和PVC

如果需要永久保存数据（当pod删除后数据不会丢失），我们需要使用PV（PersistentVolume），和PVC（PersistentVolumeClaim）的方式。

在Ceph集群中创建images

rbd create -s 1024 k8s/pvrbd feature disable k8s/pv object-map fast-diff deep-flatten

查看镜像信息：

# rbd info k8s/pvrbd image 'pv':    size 1 GiB in 256 objects    order 22 (4 MiB objects)    id: adaa6b8b4567    block_name_prefix: rbd_data.adaa6b8b4567    format: 2    features: layering, exclusive-lock    op_features:     flags:     create_timestamp: Tue Apr 23 19:09:58 2019

创建一个secret

1. 生成一个加密的key

grep key /etc/ceph/ceph.client.admin.keyring |awk '{printf "%s", $NF}'|base64

2. 将生成的key创建一个Secret

apiVersion: v1kind: Secretmetadata:  name: ceph-secrettype: "kubernetes.io/rbd"  data:  key: QVFBbk1MaGNBV2laSGhBQUVOQThRWGZyQ3haRkJDNlJaWTNJY1E9PQ==---

创建PV和PVC文件

# cat ceph-rbd-pv.yaml apiVersion: v1kind: PersistentVolumemetadata:  name: ceph-rbd-pvspec:  capacity:    storage: 1Gi  accessModes:    - ReadWriteOnce  rbd:    monitors:      - '192.168.20.41:6789'    pool: k8s    image: pv    user: admin    secretRef:      name: ceph-secret    fsType: xfs    readOnly: false  persistentVolumeReclaimPolicy: Recycle# cat ceph-rbd-pvc.yaml apiVersion: v1kind: PersistentVolumeClaimmetadata:  name: ceph-rbd-pv-claimspec:  accessModes:    - ReadWriteOnce  resources:    requests:      storage: 1Gi

创建POD

# cat test3-pvc.yaml apiVersion: v1kind: Podmetadata:  name: rbd-nginxspec:  containers:    - image: nginx      name: rbd-rw      volumeMounts:      - name: rbd-pvc        mountPath: /mnt  volumes:    - name: rbd-pvc      persistentVolumeClaim:        claimName: ceph-rbd-pv-claim

使用StorageClass

Storage Class的作用

简单来说，storage配置了要访问ceph RBD的IP/Port、用户名、keyring、pool，等信息，我们不需要提前创建image；当用户创建一个PVC时，k8s查找是否有符合PVC请求的storage class类型，如果有，则依次执行如下操作：

• 到ceph集群上创建image
• 创建一个PV，名字为pvc-xx-xxx-xxx，大小pvc请求的storage。
• 将上面的PV与PVC绑定，格式化后挂到容器中

通过这种方式管理员只要创建好storage class就行了，后面的事情用户自己就可以搞定了。如果想要防止资源被耗尽，可以设置一下Resource Quota。

当pod需要一个卷时，直接通过PVC声明，就可以根据需求创建符合要求的持久卷。

创建storage class

# cat storageclass.yaml apiVersion: storage.k8s.io/v1kind: StorageClassmetadata:  name: fastprovisioner: kubernetes.io/rbdparameters:  monitors: 192.168.20.41:6789  adminId: admin  adminSecretName: ceph-secret  pool: k8s  userId: admin  userSecretName: ceph-secret  fsType: xfs  imageFormat: "2"  imageFeatures: "layering"

创建PVC

RBD只支持 ReadWriteOnce 和 ReadOnlyAll，不支持ReadWriteAll。注意这两者的区别点是，不同nodes之间是否可以同时挂载。同一个node上，即使是ReadWriteOnce，也可以同时挂载到2个容器上的。

创建应用的时候，需要同时创建 pv和pod，二者通过storageClassName关联。pvc中需要指定其storageClassName为上面创建的sc的name（即fast）。

# cat pvc.yaml kind: PersistentVolumeClaimapiVersion: v1metadata:  name: rbd-pvc-pod-pvcspec:  accessModes:    - ReadWriteOnce  volumeMode: Filesystem  resources:    requests:      storage: 1Gi  storageClassName: fast

创建pod

# cat pod.yaml apiVersion: v1kind: Podmetadata:  labels:    test: rbd-pvc-pod  name: ceph-rbd-sc-pod1spec:  containers:  - name: ceph-rbd-sc-nginx    image: nginx    volumeMounts:    - name: ceph-rbd-vol1      mountPath: /mnt      readOnly: false  volumes:  - name: ceph-rbd-vol1    persistentVolumeClaim:      claimName: rbd-pvc-pod-pvc

补充

在使用Storage Class时，除了使用PVC的方式声明要使用的持久卷，还可通过创建一个volumeClaimTemplates进行声明创建（StatefulSets中的存储设置），如果涉及到多个副本，可以使用StatefulSets配置：

apiVersion: apps/v1kind: StatefulSetmetadata:  name: nginxspec:  selector:    matchLabels:      app: nginx  serviceName: "nginx"  replicas: 3  template:    metadata:      labels:        app: nginx    spec:      terminationGracePeriodSeconds: 10      containers:      - name: nginx        image: nginx        volumeMounts:        - name: www          mountPath: /usr/share/nginx/html  volumeClaimTemplates:  - metadata:      name: www    spec:      accessModes: [ "ReadWriteOnce" ]      storageClassName: "fast"      resources:        requests:          storage: 1Gi

但注意不要用Deployment。因为，如果Deployment的副本数是1，那么还是可以用的，跟Pod一致；但如果副本数 >1 ，此时创建deployment后会发现，只启动了1个Pod，其他Pod都在ContainerCreating状态。过一段时间describe pod可以看到，等volume等很久都没等到。

示例一:创建一个mysql-galera集群（多主）

官方文档：https://kubernetes.io/docs/tasks/run-application/run-replicated-stateful-application/

statefulset简介

statefulset(1.5之前叫做petset),statefulset与deployment,replicasets是一个级别的。不过Deployments和ReplicaSets是为无状态服务而设计。statefulset则是为了解决有状态服务的问题。它的应用场景如下：

• 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
• 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。
• 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。
• 有序收缩，有序删除（即从N-1到0）。

由应用场景可知，statefuleset特别适合mqsql,redis等数据库集群。相应的，一个statefuleset有以下三个部分：

• 用于定义网络标志（DNS domain）的HeadlessService，参考文档 ）
• 用于创建PersistentVolumes的volumeClaimTemplates
• 定义具体应用的StatefulSet

1. 生成并创建ceph secret

如果k8s集群中已经创建了ceph 的secret可以跳过此步

生成一个加密的key

grep key /etc/ceph/ceph.client.admin.keyring |awk '{printf "%s", $NF}'|base64

将生成的key创建一个Secret

apiVersion: v1kind: Secretmetadata:  name: ceph-secret  namespace: galeratype: "kubernetes.io/rbd"  data:  key: QVFBbk1MaGNBV2laSGhBQUVOQThRWGZyQ3haRkJDNlJaWTNJY1E9PQ==---

2. 创建StorageClass

# cat storageclass.yaml apiVersion: storage.k8s.io/v1kind: StorageClassmetadata:  name: fastprovisioner: kubernetes.io/rbdparameters:  monitors: 192.168.20.41:6789,192.168.20.42:6789,192.168.20.43:6789  adminId: admin  adminSecretName: ceph-secret  pool: k8s  userId: admin  userSecretName: ceph-secret  fsType: xfs  imageFormat: "2"  imageFeatures: "layering"

3. 创建headless Service

galera-service.yaml

apiVersion: v1kind: Servicemetadata:  annotations:    service.alpha.kubernetes.io/tolerate-unready-endpoints: "true"  name: galera  namespace: galera  labels:    app: mysqlspec:  ports:  - port: 3306    name: mysql  # *.galear.default.svc.cluster.local  clusterIP: None  selector:    app: mysql

4. 创建statefulset

这里使用V1版本的StatefulSet，和之前的版本相比，v1版本是当前的稳定版本，同时与之前的beta版的区别是v1版本需要添加spec.selector.matchLabels的参数，此参数需要与spec.template.metadata.labels保持一致。

apiVersion: apps/v1kind: StatefulSetmetadata:  name: mysql  namespace: galeraspec:  selector:    matchLabels:      app: mysql  serviceName: "galera"  replicas: 3  template:    metadata:      labels:        app: mysql    spec:      initContainers:      - name: install        image: mirrorgooglecontainers/galera-install:0.1        imagePullPolicy: Always        args:        - "--work-dir=/work-dir"        volumeMounts:        - name: workdir          mountPath: "/work-dir"        - name: config          mountPath: "/etc/mysql"      - name: bootstrap        image: debian:jessie        command:        - "/work-dir/peer-finder"        args:        - -on-start="/work-dir/on-start.sh"        - "-service=galera"        env:        - name: POD_NAMESPACE          valueFrom:            fieldRef:              apiVersion: v1              fieldPath: metadata.namespace        volumeMounts:        - name: workdir          mountPath: "/work-dir"        - name: config          mountPath: "/etc/mysql"      containers:      - name: mysql        image: mirrorgooglecontainers/mysql-galera:e2e        ports:        - containerPort: 3306          name: mysql        - containerPort: 4444          name: sst        - containerPort: 4567          name: replication        - containerPort: 4568          name: ist        args:        - --defaults-file=/etc/mysql/my-galera.cnf        - --user=root        readinessProbe:          # TODO: If docker exec is buggy just use gcr.io/google_containers/mysql-healthz:1.0          exec:            command:            - sh            - -c            - "mysql -u root -e 'show databases;'"          initialDelaySeconds: 15          timeoutSeconds: 5          successThreshold: 2        volumeMounts:        - name: datadir          mountPath: /var/lib/        - name: config          mountPath: /etc/mysql      volumes:      - name: config        emptyDir: {}      - name: workdir        emptyDir: {}  volumeClaimTemplates:  - metadata:      name: datadir      annotations:        volume.beta.kubernetes.io/storage-class: "fast"    spec:      accessModes: [ "ReadWriteOnce" ]      resources:        requests:          storage: 1Gi

5. 检查pod

查看pod状态已经正常

[root@master-1 ~]# kubectl  get pod  -n galera NAME      READY   STATUS    RESTARTS   AGEmysql-0   1/1     Running   0          48mmysql-1   1/1     Running   0          43mmysql-2   1/1     Running   0          38m

数据库集群建立：

[root@master-1 ~]# kubectl exec mysql-1  -n galera  -- mysql -uroot -e 'show status like "wsrep_cluster_size";'Variable_name   Valuewsrep_cluster_size  3

查看pv绑定：

[root@master-1 mysql-cluster]# kubectl get pvc -l app=mysql -n galeraNAME              STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGEdatadir-mysql-0   Bound    pvc-6e5a1c45-666b-11e9-ad20-000c29016590   1Gi        RWO            fast           3d20hdatadir-mysql-1   Bound    pvc-25683cfd-666c-11e9-ad20-000c29016590   1Gi        RWO            fast           3d20hdatadir-mysql-2   Bound    pvc-c024b422-666c-11e9-ad20-000c29016590   1Gi        RWO            fast           3d20h

测试数据库:

kubectl  exec mysql-2 -n galera -- mysql -uroot -e <

查看数据：

# kubectl run mysql-client --image=mysql:5.7 -i -t --rm --restart=Never --  mysql -h 10.2.58.7 -e "SELECT * FROM demo.messages"If you don't see a command prompt, try pressing enter.+---------+| message |+---------+| hello   |+---------+pod "mysql-client" deleted

定义集群内部访问数据库

如果pod之间互相访问，查询数据库就需要定义一个svc, 这里定义一个连接mysql的svc:

apiVersion: v1kind: Servicemetadata:  name: mysql-read  namespace: galera  labels:    app: mysqlspec:  ports:  - name: mysql    port: 3306  selector:    app: mysql

通过使用Pod来访问数据库：

# kubectl run mysql-client --image=mysql:5.7 -i -t --rm --restart=Never --  mysql -h mysql-read.galera -e "SELECT * FROM demo.messages"+---------+| message |+---------+| hello   |+---------+pod "mysql-client" deleted

示例二: 部署mysql主从集群

官方参考文档

1. ceph集群中创建pool

在ceph 集群中创建一个kube的pool,用于数据库的存储池：

[root@ceph-1 ~]# ceph osd pool create kube 128pool 'kube' created

2. 使用之前创建的secretkey创建Storageclass

新定义一个storageclass:

apiVersion: storage.k8s.io/v1kind: StorageClassmetadata:  name: mysqlprovisioner: kubernetes.io/rbdparameters:  monitors: 192.168.20.41:6789,192.168.20.42:6789,192.168.20.43:6789  adminId: admin  adminSecretName: ceph-secret  pool: kube  userId: admin  userSecretName: ceph-secret  fsType: xfs  imageFormat: "2"  imageFeatures: "layering"

3. 创建headless Service

由于要使用statefulSet进行主从数据库的部署，这里需要创建一个headless的service,和一个用于读库的service：

# Headless service for stable DNS entries of StatefulSet members.apiVersion: v1kind: Servicemetadata:  name: mysql  labels:    app: mysqlspec:  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: v1kind: Servicemetadata:  name: mysql-read  labels:    app: mysqlspec:  ports:  - name: mysql    port: 3306  selector:    app: mysql

4. 创建用于主从同步的配置文件configmap

由于要进行主从同步，所以必须主库和从库必须要有相应的配置：

apiVersion: v1kind: ConfigMapmetadata:  name: mysql  labels:    app: mysqldata:  master.cnf: |    # Apply this config only on the master.    [mysqld]    log-bin  slave.cnf: |    # Apply this config only on slaves.    [mysqld]    super-read-only

5 创建statefulSet

这里指定了使用StorageClass，使用RBD存储，同时需要使用一个xtrabackup的镜像进行数据同步：

apiVersion: apps/v1kind: StatefulSetmetadata:  name: mysqlspec:  selector:    matchLabels:      app: mysql  serviceName: mysql  replicas: 3  template:    metadata:      labels:        app: 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 [[ $ordinal -eq 0 ]]; then            cp /mnt/config-map/master.cnf /mnt/conf.d/          else            cp /mnt/config-map/slave.cnf /mnt/conf.d/          fi        volumeMounts:        - name: conf          mountPath: /mnt/conf.d        - name: config-map          mountPath: /mnt/config-map      - name: clone-mysql        image: tangup/xtrabackup:1.0        command:        - bash        - "-c"        - |          set -ex          # Skip the clone if data already exists.          [[ -d /var/lib/mysql/mysql ]] && exit 0          # Skip the clone on master (ordinal index 0).          [[ `hostname` =~ -([0-9]+)$ ]] || 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        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: tangup/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 ]]; then            # XtraBackup already generated a partial "CHANGE MASTER TO" query            # because we're cloning from an existing slave.            mv xtrabackup_slave_info change_master_to.sql.in            # Ignore xtrabackup_binlog_info in this case (it's useless).            rm -f 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 xtrabackup_binlog_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"            # In case of container restart, attempt this at-most-once.            mv change_master_to.sql.in change_master_to.sql.orig            mysql -h 127.0.0.1 <

6. 检查集群状态

查看pod:

[root@master-1 ~]# kubectl  get poNAME      READY   STATUS    RESTARTS   AGEmysql-0   2/2     Running   2          110mmysql-1   2/2     Running   0          109mmysql-2   2/2     Running   0          16m

pvc：

[root@master-1 ~]# kubectl get pvc |grep mysql|grep -v fastdata-mysql-0        Bound    pvc-3737108a-6a2a-11e9-ac56-000c296b46ac   1Gi        RWO            mysql          5h53mdata-mysql-1        Bound    pvc-279bdca0-6a4a-11e9-ac56-000c296b46ac   1Gi        RWO            mysql          114mdata-mysql-2        Bound    pvc-fbe153bc-6a52-11e9-ac56-000c296b46ac   1Gi        RWO            mysql          51m

Ceph集群上自动创建的镜像：

[root@ceph-1 ~]# rbd list kubekubernetes-dynamic-pvc-2ee47370-6a4a-11e9-bb82-000c296b46ackubernetes-dynamic-pvc-39a42869-6a2a-11e9-bb82-000c296b46ackubernetes-dynamic-pvc-fbead120-6a52-11e9-bb82-000c296b46ac

7.测试数据库集群

向主库写入数据，使用headless server所提供的 podname.headlessname 的形式就可以直接访问POD， 这在DNS解析中是固定的。这里访问mysql-0就使用mysql-0.mysql:

kubectl run mysql-client --image=mysql:5.7 -i --rm --restart=Never --\  mysql -h mysql-0.mysql <

使用mysql-read去访问数据库数据：

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

可以使用如下命令去循环的查看当前是mysql-read连接的数据库：

kubectl run mysql-client-loop --image=mysql:5.7 -i -t --rm --restart=Never --\  bash -ic "while sleep 1; do mysql -h mysql-read -e 'SELECT @@server_id,NOW()'; done"  +-------------+---------------------+| @@server_id | NOW()               |+-------------+---------------------+|         102 | 2019-04-28 20:24:11 |+-------------+---------------------++-------------+---------------------+| @@server_id | NOW()               |+-------------+---------------------+|         101 | 2019-04-28 20:27:35 |+-------------+---------------------++-------------+---------------------+| @@server_id | NOW()               |+-------------+---------------------+|         100 | 2019-04-28 20:18:38 |+-------------+---------------------+