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.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
To check the version, enter kubectl version
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GCEPersistentDisk
. GCEPersistentDisk
卷只能工作在Google Compute Engine平台上.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
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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
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
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部署YAML文件中定义的内容:
kubectl create -f https://k8s.io/docs/tasks/run-application/mysql-deployment.yaml
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
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
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.
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.
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>
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:
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.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
了解更多Deployment对象请参考 Deployment objects.
了解更多Deployment应用请参考 Deploying applications
kubectl run文档请参考kubectl run documentation
卷和持久卷请参考Volumes and Persistent Volumes
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