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运行一个单实例有状态应用

本文介绍在Kubernetes中使用PersistentVolume和Deployment如何运行一个单实例有状态应用. 该应用是MySQL.

Objectives

Before you begin

To check the version, enter kubectl version.

在环境中设置一个磁盘

你可以为有状态的应用使用任何类型的持久卷. 有关支持环境的磁盘列表，请参考持久卷类型Types of Persistent Volumes. 对于Google Compute Engine, 请运行:

gcloud compute disks create --size=20GB mysql-disk

接下来创建一个指向刚创建的 mysql-disk磁盘的PersistentVolume. 下面是一个PersistentVolume的配置文件，它指向上面创建的Compute Engine磁盘:

gce-volume.yaml docs/tasks/run-application 
apiVersion: v1
kind: PersistentVolume
metadata:
  name: mysql-pv
spec:
  capacity:
    storage: 20Gi
  accessModes:
    - ReadWriteOnce
  gcePersistentDisk:
    pdName: mysql-disk
    fsType: ext4

注意pdName: mysql-disk 这行与Compute Engine环境中的磁盘名称相匹配. 有关为其 他环境编写PersistentVolume配置文件的详细信息，请参见持久卷Persistent Volumes.

创建持久卷:

kubectl create -f https://k8s.io/docs/tasks/run-application/gce-volume.yaml

部署MySQL

通过创建Kubernetes Deployment并使用PersistentVolumeClaim将其连接到现已存在的PersistentVolume上来运行一个有状态的应用. 例如, 下面这个YAML文件描述了一个运行MySQL 并引用PersistentVolumeClaim的Deployment. 该文件定义了一个volume其挂载目录为/var/lib/mysql, 然后创建一个内存为20G的卷的PersistentVolumeClaim. 此申领可以通过任 何符合需求的卷来满足, 在本例中满足上面创建的卷.

注意: 在配置的yaml文件中定义密码的做法是不安全的. 具体安全解决方案请参考 Kubernetes Secrets.

mysql-deployment.yaml docs/tasks/run-application 
apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  ports:
  - port: 3306
  selector:
    app: mysql
  clusterIP: None
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-pv-claim
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: ""
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: mysql
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
          # Use secret in real usage
        - name: MYSQL_ROOT_PASSWORD
          value: password
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim

  1. 部署YAML文件中定义的内容:

    kubectl create -f https://k8s.io/docs/tasks/run-application/mysql-deployment.yaml

  2. 展示Deployment相关信息:

    kubectl describe deployment mysql

    Name:                 mysql
Namespace:            default
CreationTimestamp:    Tue, 01 Nov 2016 11:18:45 -0700
Labels:               app=mysql
Annotations:          deployment.kubernetes.io/revision=1
Selector:             app=mysql
Replicas:             1 desired | 1 updated | 1 total | 0 available | 1 unavailable
StrategyType:         Recreate
MinReadySeconds:      0
Pod Template:
  Labels:       app=mysql
  Containers:
   mysql:
    Image:      mysql:5.6
    Port:       3306/TCP
    Environment:
      MYSQL_ROOT_PASSWORD:      password
    Mounts:
      /var/lib/mysql from mysql-persistent-storage (rw)
  Volumes:
   mysql-persistent-storage:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  mysql-pv-claim
    ReadOnly:   false
Conditions:
  Type          Status  Reason
  ----          ------  ------
  Available     False   MinimumReplicasUnavailable
  Progressing   True    ReplicaSetUpdated
OldReplicaSets:       <none>
NewReplicaSet:        mysql-63082529 (1/1 replicas created)
Events:
  FirstSeen    LastSeen    Count    From                SubobjectPath    Type        Reason            Message
  ---------    --------    -----    ----                -------------    --------    ------            -------
  33s          33s         1        {deployment-controller }             Normal      ScalingReplicaSet Scaled up replica set mysql-63082529 to 1

  3. 列举出Deployment创建的pods:

    kubectl get pods -l app=mysql

    NAME                   READY     STATUS    RESTARTS   AGE
mysql-63082529-2z3ki   1/1       Running   0          3m

  4. 查看持久卷:

    kubectl describe pv mysql-pv

    Name:            mysql-pv
Labels:          <none>
Status:          Bound
Claim:           default/mysql-pv-claim
Reclaim Policy:  Retain
Access Modes:    RWO
Capacity:        20Gi
Message:
Source:
    Type:        GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
    PDName:      mysql-disk
    FSType:      ext4
    Partition:   0
    ReadOnly:    false
No events.

  5. 查看PersistentVolumeClaim:

    kubectl describe pvc mysql-pv-claim

    Name:         mysql-pv-claim
Namespace:    default
Status:       Bound
Volume:       mysql-pv
Labels:       <none>
Capacity:     20Gi
Access Modes: RWO
No events.

访问MySQL实例

前面YAML文件中创建了一个允许集群内其他pods访问数据库的服务. 该服务中选项 clusterIP: None 让服务DNS名称直接解析为Pod的IP地址. 当在一个服务下只有一个pod 并且不打算增加pods的数量这是最好的.

运行MySQL客户端以连接到服务器:

kubectl run -it --rm --image=mysql:5.6 mysql-client -- mysql -h <pod-ip> -p <password>

此命令在集群内创建一个新的Pod并运行MySQL客户端,并通过服务将其连接到服务器.如果连接成功,你就知道有状态的MySQL database正处于运行状态.

Waiting for pod default/mysql-client-274442439-zyp6i to be running, status is Pending, pod ready: false
If you don't see a command prompt, try pressing enter.

mysql>

更新

Deployment中镜像或其他部分同往常一样可以通过 kubectl apply 命令更新. 以下是 特定于有状态应用的一些注意事项:

删除deployment

通过名称删除部署的对象:

kubectl delete deployment,svc mysql
kubectl delete pvc mysql-pv-claim
kubectl delete pv mysql-pv

如果使用Compute Engine磁盘，也可以使用如下命令:

gcloud compute disks delete mysql-disk

What's next