Kubernetes 201

扩展应用

通过修改 Deployment 中副本的数量(replicas),可以动态扩展或收缩应用:
scale
这些自动扩展的容器会自动加入到 service 中,而收缩回收的容器也会自动从 service 中删除。
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$ kubectl scale --replicas=3 deployment/nginx-app
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$ kubectl get deploy
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NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
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nginx-app 3 3 3 3 10m
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滚动升级

滚动升级(Rolling Update)通过逐个容器替代升级的方式来实现无中断的服务升级:
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kubectl rolling-update frontend-v1 frontend-v2 --image=image:v2
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update1
update2
update3
update4
在滚动升级的过程中,如果发现了失败或者配置错误,还可以随时回滚:
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kubectl rolling-update frontend-v1 frontend-v2 --rollback
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需要注意的是,kubectl rolling-update 只针对 ReplicationController。对于更新策略是 RollingUpdate 的 Deployment(Deployment 可以在 spec 中设置更新策略为 RollingUpdate,默认就是 RollingUpdate),更新应用后会自动滚动升级:
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spec:
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replicas: 3
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selector:
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matchLabels:
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run: nginx-app
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strategy:
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rollingUpdate:
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maxSurge: 1
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maxUnavailable: 1
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type: RollingUpdate
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而更新应用的话,就可以直接用 kubectl set 命令:
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kubectl set image deployment/nginx-app nginx-app=nginx:1.9.1
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滚动升级的过程可以用 rollout 命令查看:
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$ kubectl rollout status deployment/nginx-app
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Waiting for rollout to finish: 2 out of 3 new replicas have been updated...
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Waiting for rollout to finish: 2 of 3 updated replicas are available...
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Waiting for rollout to finish: 2 of 3 updated replicas are available...
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Waiting for rollout to finish: 2 of 3 updated replicas are available...
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Waiting for rollout to finish: 2 of 3 updated replicas are available...
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Waiting for rollout to finish: 2 of 3 updated replicas are available...
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deployment "nginx-app" successfully rolled out
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Deployment 也支持回滚:
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$ kubectl rollout history deployment/nginx-app
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deployments "nginx-app"
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REVISION CHANGE-CAUSE
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1 <none>
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2 <none>
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$ kubectl rollout undo deployment/nginx-app
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deployment "nginx-app" rolled back
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资源限制

Kubernetes 通过 cgroups 提供容器资源管理的功能,可以限制每个容器的 CPU 和内存使用,比如对于刚才创建的 deployment,可以通过下面的命令限制 nginx 容器最多只用 50% 的 CPU 和 128MB 的内存:
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$ kubectl set resources deployment nginx-app -c=nginx --limits=cpu=500m,memory=128Mi
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deployment "nginx" resource requirements updated
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这等同于在每个 Pod 中设置 resources limits:
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apiVersion: v1
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kind: Pod
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metadata:
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labels:
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app: nginx
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name: nginx
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spec:
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containers:
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- image: nginx
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name: nginx
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resources:
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limits:
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cpu: "500m"
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memory: "128Mi"
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健康检查

Kubernetes 作为一个面向应用的集群管理工具,需要确保容器在部署后确实处在正常的运行状态。Kubernetes 提供了两种探针(Probe,支持 exec、tcpSocket 和 http 方式)来探测容器的状态:
  • LivenessProbe:探测应用是否处于健康状态,如果不健康则删除并重新创建容器
  • ReadinessProbe:探测应用是否启动完成并且处于正常服务状态,如果不正常则不会接收来自 Kubernetes Service 的流量
对于已经部署的 deployment,可以通过 kubectl edit deployment/nginx-app 来更新 manifest,增加健康检查部分:
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apiVersion: extensions/v1beta1
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kind: Deployment
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metadata:
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labels:
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app: nginx
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name: nginx-default
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spec:
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replicas: 3
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selector:
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matchLabels:
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app: nginx
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template:
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metadata:
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labels:
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app: nginx
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spec:
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containers:
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- image: nginx
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imagePullPolicy: Always
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name: http
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resources: {}
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terminationMessagePath: /dev/termination-log
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terminationMessagePolicy: File
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resources:
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limits:
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cpu: "500m"
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memory: "128Mi"
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livenessProbe:
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httpGet:
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path: /
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port: 80
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initialDelaySeconds: 15
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timeoutSeconds: 1
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readinessProbe:
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httpGet:
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path: /
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port: 80
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initialDelaySeconds: 5
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timeoutSeconds: 1
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最近更新 2yr ago