website/content/zh/docs/tasks/run-application/run-single-instance-stateful-application.md

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title: 运行一个单实例有状态应用
content_template: templates/tutorial
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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.

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* 在环境中通过磁盘创建一个PersistentVolume.
* 创建一个MySQL Deployment.
* 在集群内以一个已知的 DNS 名将 MySQL 暴露给其他 pods.

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## 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](/docs/concepts/configuration/secret/).

{{< codenew file="application/mysql/mysql-deployment.yaml" >}}
{{< codenew file="application/mysql/mysql-pv.yaml" >}}

1. 部署 YAML 文件中定义的 PV 和 PVC：

        kubectl apply -f https://k8s.io/examples/application/mysql/mysql-pv.yaml

1. 部署 YAML 文件中定义的 Deployment：

        kubectl apply -f https://k8s.io/examples/application/mysql/mysql-deployment.yaml

1. 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


1. 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


1. 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.


1. 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:

* 不要弹性伸缩. 弹性伸缩仅适用于单实例应用. 下层的PersistentVolume仅只能挂载一个pod. 对于集群级有状态应用, 请参考StatefulSet文档
  [StatefulSet documentation](/docs/concepts/workloads/controllers/statefulset/).
* 在Deployment的YAML文件中使用 `strategy:` `type: Recreate` . 该选项指示Kubernetes不使用滚动升级. 滚动升级将无法工作, 由于一次不能运行多个pod. 在更新配置文件
创建一个新的pod前 `Recreate`策略将先停止第一个pod.


## 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
```

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* 了解更多Deployment对象请参考 [Deployment objects](/docs/concepts/workloads/controllers/deployment/).

* 了解更多Deployment应用请参考 [Deploying applications](/docs/user-guide/deploying-applications/)

* kubectl run文档请参考[kubectl run documentation](/docs/user-guide/kubectl/v1.6/#run)

* 卷和持久卷请参考[Volumes](/docs/concepts/storage/volumes/) and [Persistent Volumes](/docs/concepts/storage/persistent-volumes/)

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