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除了创建，Deployment 提供的另一个重要的功能就是更新应用，这是一个比创建复杂很多的过程。想象一下在日常交付中，在线升级是一个很常见的需求，同时应该尽量保证不能因为升级中断服务。这就要求我们必须使用一定的策略来决定何时创建新的 Pod，何时删除旧版本的 Pod。kubectl 支持滚动升级的方式，每次更新一个pod，而不是同时删除整个服务。
回顾知识：
命令格式：
kubectl set image (-f FILENAME | TYPE NAME) CONTAINER_NAME_1=CONTAINER_IMAGE_1 ... CONTAINER_NAME_N=CONTAINER_IMAGE_N例如：
Examples: # Set a deployment's nginx container image to 'nginx:1.9.1', and its busybox container image to 'busybox'. kubectl set image deployment/nginx busybox=busybox nginx=nginx:1.9.1 # Update all deployments' and rc's nginx container's image to 'nginx:1.9.1' kubectl set image deployments,rc nginx=nginx:1.9.1 --all # Update image of all containers of daemonset abc to 'nginx:1.9.1' kubectl set image daemonset abc *=nginx:1.9.1 # Print result (in yaml format) of updating nginx container image from local file, without hitting the server kubectl set image -f path/to/file.yaml nginx=nginx:1.9.1 --local -o yaml??Tips：支持缩写，如pod (po), replicationcontroller (rc), deployment (deploy), daemonset (ds), replicaset (rs)。
--all=false: Select all resources, including uninitialized ones, in the namespace of the specified resource types --allow-missing-template-keys=true: If true, ignore any errors in templates when a field or map key is missing inthe template. Only applies to golang and jsonpath output formats. --dry-run='none': Must be "none", "server", or "client". If client strategy, only print the object that would besent, without sending it. If server strategy, submit server-side request without persisting the resource. --field-manager='kubectl-set': Name of the manager used to track field ownership. -f, --filename=[]: Filename, directory, or URL to files identifying the resource to get from a server. -k, --kustomize='': Process the kustomization directory. This flag can't be used together with -f or -R. --local=false: If true, set image will NOT contact api-server but run locally. -o, --output='': Output format. One of:json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-as-json|jsonpath-file. --record=false: Record current kubectl command in the resource annotation. If set to false, do not record thecommand. If set to true, record the command. If not set, default to updating the existing annotation value only if onealready exists. -R, --recursive=false: Process the directory used in -f, --filename recursively. Useful when you want to managerelated manifests organized within the same directory. -l, --selector='': Selector (label query) to filter on, not including uninitialized ones, supports '=', '==', and'!='.(e.g. -l key1=value1,key2=value2) --show-managed-fields=false: If true, keep the managedFields when printing objects in JSON or YAML format. --template='': Template string or path to template file to use when -o=go-template, -o=go-template-file. Thetemplate format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].先创建一个deployment，ngx-deploy.yaml配置文件如下：
apiVersion: apps/v1kind: Deploymentmetadata: name: nginx-deployment labels: app: nginxspec: replicas: 2 selector: matchLabels: app: nginx template: metadata: labels: app: nginx spec: containers: - name: nginx image: nginx:1.16.0 ports: - containerPort: 80执行命令：
kubectl create -f ngx-deploy.yaml使用 watch 方式来观测 deployment 的状态变化：
[root@master test]# kubectl get deploy nginx-deployment -wNAME READY UP-TO-DATE AVAILABLE AGEnginx-deployment 0/2 2 0 14snginx-deployment 1/2 2 1 25snginx-deployment 2/2 2 2 38s说明：
接下来先更新一个nginx镜像，版本为1.18：
kubectl set image deployment.v1.apps/nginx-deployment nginx=nginx:1.18.0 --record说明：
--record ：将这条命令记录到了 deployment 的 yaml 的 annotations 里，可用于回滚镜像。使用watch方式观察deployment实例变更情况：
[root@master test]# kubectl get deploy nginx-deployment -wNAME READY UP-TO-DATE AVAILABLE AGEnginx-deployment 2/2 1 2 3m41snginx-deployment 3/2 1 3 3m58snginx-deployment 2/2 1 2 3m58snginx-deployment 2/2 2 2 3m58s可以通过 get yaml 看到：
[root@master test]# kubectl get deploy nginx-deployment -o yaml... template: metadata: creationTimestamp: null labels: app: nginx spec: containers: - image: nginx:1.18.0 imagePullPolicy: IfNotPresent name: nginx ports: - containerPort: 80 protocol: TCP resources: {} terminationMessagePath: /dev/termination-log terminationMessagePolicy: File dnsPolicy: ClusterFirst restartPolicy: Always schedulerName: default-scheduler securityContext: {} terminationGracePeriodSeconds: 30...有更新就有回滚。比如新的镜像版本有问题，或者配置不对等等，这是部署到生产环境里经常发生的事情。相对于更新，回滚镜像一般都是出现了问题，需要更快地进行处理。Deployment 的回滚机制正是为此而生。
可以通过命令查看历史版本：
[root@master test]# kubectl rollout history deployment.v1.apps/nginx-deploymentdeployment.apps/nginx-deployment REVISION CHANGE-CAUSE1 <none>2 kubectl set image deployment.v1.apps/nginx-deployment nginx=nginx:1.18.0 --record=true回滚到上一个版本：
kubectl rollout undo deployment.v1.apps/nginx-deployment可以观察到已回到上个版本：
[root@master test]# kubectl get deploy nginx-deployment -o yaml... template: metadata: creationTimestamp: null labels: app: nginx spec: containers: - image: nginx:1.16.0 imagePullPolicy: IfNotPresent name: nginx ports: - containerPort: 80 protocol: TCP resources: {} terminationMessagePath: /dev/termination-log terminationMessagePolicy: File dnsPolicy: ClusterFirst restartPolicy: Always schedulerName: default-scheduler securityContext: {} terminationGracePeriodSeconds: 30...也可回滚到指定版本：
kubectl rollout undo deployment.v1.apps/nginx-deployment --to-revision=2