180 lines
6.1 KiB
Markdown
180 lines
6.1 KiB
Markdown
---
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title: 运行一个单实例有状态应用
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content_type: tutorial
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---
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<!-- overview -->
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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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## {{% heading "objectives" %}}
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* 在环境中通过磁盘创建一个PersistentVolume.
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* 创建一个MySQL Deployment.
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* 在集群内以一个已知的 DNS 名将 MySQL 暴露给其他 pods.
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## {{% heading "prerequisites" %}}
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* {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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* {{< include "default-storage-class-prereqs.md" >}}
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<!-- lessoncontent -->
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## 部署MySQL
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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
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[Kubernetes Secrets](/docs/concepts/configuration/secret/).
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{{< codenew file="application/mysql/mysql-deployment.yaml" >}}
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{{< codenew file="application/mysql/mysql-pv.yaml" >}}
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1. 部署 YAML 文件中定义的 PV 和 PVC：
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kubectl apply -f https://k8s.io/examples/application/mysql/mysql-pv.yaml
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1. 部署 YAML 文件中定义的 Deployment：
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kubectl apply -f https://k8s.io/examples/application/mysql/mysql-deployment.yaml
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1. 展示 Deployment 相关信息:
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kubectl describe deployment mysql
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Name: mysql
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Namespace: default
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CreationTimestamp: Tue, 01 Nov 2016 11:18:45 -0700
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Labels: app=mysql
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Annotations: deployment.kubernetes.io/revision=1
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Selector: app=mysql
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Replicas: 1 desired | 1 updated | 1 total | 0 available | 1 unavailable
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StrategyType: Recreate
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MinReadySeconds: 0
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Pod Template:
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Labels: app=mysql
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Containers:
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mysql:
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Image: mysql:5.6
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Port: 3306/TCP
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Environment:
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MYSQL_ROOT_PASSWORD: password
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Mounts:
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/var/lib/mysql from mysql-persistent-storage (rw)
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Volumes:
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mysql-persistent-storage:
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Type: PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
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ClaimName: mysql-pv-claim
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ReadOnly: false
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Conditions:
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Type Status Reason
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---- ------ ------
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Available False MinimumReplicasUnavailable
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Progressing True ReplicaSetUpdated
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OldReplicaSets: <none>
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NewReplicaSet: mysql-63082529 (1/1 replicas created)
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Events:
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FirstSeen LastSeen Count From SubobjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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33s 33s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set mysql-63082529 to 1
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1. 列举出 Deployment 创建的 pods:
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kubectl get pods -l app=mysql
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NAME READY STATUS RESTARTS AGE
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mysql-63082529-2z3ki 1/1 Running 0 3m
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1. 查看 PersistentVolumeClaim:
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kubectl describe pvc mysql-pv-claim
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Name: mysql-pv-claim
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Namespace: default
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StorageClass:
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Status: Bound
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Volume: mysql-pv-volume
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Labels: <none>
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Annotations: pv.kubernetes.io/bind-completed=yes
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pv.kubernetes.io/bound-by-controller=yes
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Capacity: 20Gi
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Access Modes: RWO
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Events: <none>
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## 访问 MySQL 实例
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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
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`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
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并且不打算增加 pods 的数量这是最好的.
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运行 MySQL 客户端以连接到服务器:
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```
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kubectl run -it --rm --image=mysql:5.6 --restart=Never mysql-client -- mysql -h mysql -ppassword
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```
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此命令在集群内创建一个新的 Pod 并运行 MySQL 客户端,并通过 Service 将其连接到服务器.如果连接成功,你就知道有状态的 MySQL 数据库正处于运行状态.
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```
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Waiting for pod default/mysql-client-274442439-zyp6i to be running, status is Pending, pod ready: false
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If you don't see a command prompt, try pressing enter.
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mysql>
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```
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## 更新
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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
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特定于有状态应用的一些注意事项:
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* 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
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[StatefulSet documentation](/docs/concepts/workloads/controllers/statefulset/).
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* 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
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创建一个新的 pod 前 `Recreate` 策略将先停止第一个 pod.
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## 删除 Deployment
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通过名称删除部署的对象:
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```
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kubectl delete deployment,svc mysql
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kubectl delete pvc mysql-pv-claim
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kubectl delete pv mysql-pv-volume
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```
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如果通过手动的方式分配 PersistentVolume, 那么也需要手动的删除它，以及释放下层资源.
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如果是用过动态分配 PersistentVolume 的方式，在删除 PersistentVolumeClaim 后 PersistentVolume 将被自动的删除. 一些存储服务(比如 EBS 和 PD)也会在 PersistentVolume 被删除时自动回收下层资源.
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## {{% heading "whatsnext" %}}
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* 了解更多 Deployment 对象请参考 [Deployment objects](/docs/concepts/workloads/controllers/deployment/).
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* 了解更多 Deployment 应用请参考 [Deploying applications](/docs/user-guide/deploying-applications/)
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* kubectl run 文档请参考[kubectl run documentation](/docs/reference/generated/kubectl/kubectl-commands/#run)
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* 卷和持久卷请参考 [Volumes](/docs/concepts/storage/volumes/) 和 [Persistent Volumes](/docs/concepts/storage/persistent-volumes/)
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