350 lines
12 KiB
Markdown
350 lines
12 KiB
Markdown
---
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title: 使用 Service 把前端连接到后端
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content_type: tutorial
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weight: 70
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---
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<!--
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title: Connect a Frontend to a Backend Using Services
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content_type: tutorial
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weight: 70
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-->
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<!-- overview -->
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<!--
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This task shows how to create a _frontend_ and a _backend_ microservice. The backend
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microservice is a hello greeter. The frontend exposes the backend using nginx and a
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Kubernetes {{< glossary_tooltip term_id="service" >}} object.
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-->
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本任务会描述如何创建前端（Frontend）微服务和后端（Backend）微服务。后端微服务是一个 hello 欢迎程序。
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前端通过 nginx 和一个 Kubernetes {{< glossary_tooltip term_id="service" text="服务" >}}
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暴露后端所提供的服务。
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## {{% heading "objectives" %}}
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<!--
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* Create and run a sample `hello` backend microservice using a
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{{< glossary_tooltip term_id="deployment" >}} object.
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* Use a Service object to send traffic to the backend microservice's multiple replicas.
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* Create and run a `nginx` frontend microservice, also using a Deployment object.
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* Configure the frontend microservice to send traffic to the backend microservice.
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* Use a Service object of `type=LoadBalancer` to expose the frontend microservice
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outside the cluster.
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-->
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* 使用部署对象（Deployment object）创建并运行一个 `hello` 后端微服务
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* 使用一个 Service 对象将请求流量发送到后端微服务的多个副本
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* 同样使用一个 Deployment 对象创建并运行一个 `nginx` 前端微服务
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* 配置前端微服务将请求流量发送到后端微服务
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* 使用 `type=LoadBalancer` 的 Service 对象将全段微服务暴露到集群外部
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## {{% heading "prerequisites" %}}
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{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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<!--
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This task uses
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[Services with external load balancers](/docs/tasks/access-application-cluster/create-external-load-balancer/), which
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require a supported environment. If your environment does not support this, you can use a Service of type
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[NodePort](/docs/concepts/services-networking/service/#nodeport) instead.
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-->
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本任务使用[外部负载均衡服务](/zh/docs/tasks/access-application-cluster/create-external-load-balancer/)，
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所以需要对应的可支持此功能的环境。如果你的环境不能支持，你可以使用
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[NodePort](/zh/docs/concepts/services-networking/service/#nodeport)
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类型的服务代替。
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<!-- lessoncontent -->
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<!--
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## Creating the backend using a Deployment
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The backend is a simple hello greeter microservice. Here is the configuration
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file for the backend Deployment:
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-->
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### 使用部署对象（Deployment）创建后端
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后端是一个简单的 hello 欢迎微服务应用。这是后端应用的 Deployment 配置文件：
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{{< codenew file="service/access/backend-deployment.yaml" >}}
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<!--
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Create the backend Deployment:
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-->
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创建后端 Deployment：
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```shell
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kubectl apply -f https://k8s.io/examples/service/access/backend-deployment.yaml
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```
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<!--
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View information about the backend Deployment:
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-->
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查看后端的 Deployment 信息：
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```shell
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kubectl describe deployment hello
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```
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<!--
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The output is similar to this:
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-->
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输出类似于：
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```
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Name: backend
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Namespace: default
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CreationTimestamp: Mon, 24 Oct 2016 14:21:02 -0700
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Labels: app=hello
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tier=backend
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track=stable
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Annotations: deployment.kubernetes.io/revision=1
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Selector: app=hello,tier=backend,track=stable
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Replicas: 3 desired | 3 updated | 3 total | 3 available | 0 unavailable
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StrategyType: RollingUpdate
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MinReadySeconds: 0
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RollingUpdateStrategy: 1 max unavailable, 1 max surge
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Pod Template:
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Labels: app=hello
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tier=backend
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track=stable
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Containers:
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hello:
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Image: "gcr.io/google-samples/hello-go-gke:1.0"
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Port: 80/TCP
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Environment: <none>
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Mounts: <none>
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Volumes: <none>
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Conditions:
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Type Status Reason
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---- ------ ------
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Available True MinimumReplicasAvailable
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Progressing True NewReplicaSetAvailable
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OldReplicaSets: <none>
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NewReplicaSet: hello-3621623197 (3/3 replicas created)
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Events:
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...
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```
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<!--
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## Creating the `hello` Service object
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The key to sending requests from a frontend to a backend is the backend
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Service. A Service creates a persistent IP address and DNS name entry
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so that the backend microservice can always be reached. A Service uses
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{{< glossary_tooltip text="selectors" term_id="selector" >}} to find
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the Pods that it routes traffic to.
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First, explore the Service configuration file:
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-->
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### 创建 `hello` Service 对象
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将请求从前端发送到到后端的关键是后端 Service。Service 创建一个固定 IP 和 DNS 解析名入口，
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使得后端微服务总是可达。Service 使用
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{{< glossary_tooltip text="选择算符" term_id="selector" >}}
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来寻找目标 Pod。
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首先，浏览 Service 的配置文件：
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{{< codenew file="service/access/backend-service.yaml" >}}
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<!--
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In the configuration file, you can see that the Service named `hello` routes
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traffic to Pods that have the labels `app: hello` and `tier: backend`.
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-->
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配置文件中，你可以看到名为 `hello` 的 Service 将流量路由到包含 `app: hello`
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和 `tier: backend` 标签的 Pod。
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<!--
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Create the backend Service:
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-->
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创建后端 Service：
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```shell
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kubectl apply -f https://k8s.io/examples/service/access/backend-service.yaml
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```
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<!--
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At this point, you have a `backend` Deployment running three replicas of your `hello`
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application, and you have a Service that can route traffic to them. However, this
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service is neither available nor resolvable outside the cluster.
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-->
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此时，你已经有了一个运行着 `hello` 应用的三个副本的 `backend` Deployment，你也有了
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一个 Service 用于路由网络流量。不过，这个服务在集群外部无法访问也无法解析。
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<!--
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## Creating the frontend
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Now that you have your backend running, you can create a frontend that is accessible
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outside the cluster, and connects to the backend by proxying requests to it.
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The frontend sends requests to the backend worker Pods by using the DNS name
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given to the backend Service. The DNS name is `hello`, which is the value
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of the `name` field in the `examples/service/access/backend-service.yaml`
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configuration file.
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The Pods in the frontend Deployment run an nginx image that is configured
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to proxy requests to the hello backend Service. Here is the nginx configuration file:
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-->
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### 创建前端应用
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现在你已经有了运行中的后端应用，你可以创建一个可在集群外部访问的前端，并通过代理
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前端的请求连接到后端。
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前端使用被赋予后端 Service 的 DNS 名称将请求发送到后端工作 Pods。这一 DNS
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名称为 `hello`，也就是 `examples/service/access/backend-service.yaml` 配置
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文件中 `name` 字段的取值。
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前端 Deployment 中的 Pods 运行一个 nginx 镜像，这个已经配置好的镜像会将请求转发
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给后端的 hello Service。下面是 nginx 的配置文件：
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{{< codenew file="service/access/frontend-nginx.conf" >}}
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<!--
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Similar to the backend, the frontend has a Deployment and a Service. An important
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difference to notice between the backend and frontend services, is that the
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configuration for the frontend Service has `type: LoadBalancer`, which means that
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the Service uses a load balancer provisioned by your cloud provider and will be
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accessible from outside the cluster.
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-->
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与后端类似，前端用包含一个 Deployment 和一个 Service。后端与前端服务之间的一个
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重要区别是前端 Service 的配置文件包含了 `type: LoadBalancer`，也就是说，Service
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会使用你的云服务商的默认负载均衡设备，从而实现从集群外访问的目的。
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{{< codenew file="service/access/frontend-service.yaml" >}}
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{{< codenew file="service/access/frontend-deployment.yaml" >}}
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<!--
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Create the frontend Deployment and Service:
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-->
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创建前端 Deployment 和 Service：
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```shell
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kubectl apply -f https://k8s.io/examples/service/access/frontend-deployment.yaml
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kubectl apply -f https://k8s.io/examples/service/access/frontend-service.yaml
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```
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<!--
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The output verifies that both resources were created:
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-->
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通过输出确认两个资源都已经被创建：
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```
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deployment.apps/frontend created
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service/frontend created
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```
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<!--
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The nginx configuration is baked into the
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[container image](/examples/service/access/Dockerfile). A better way to do this would
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be to use a
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[ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/),
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so that you can change the configuration more easily.
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-->
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{{< note >}}
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这个 nginx 配置文件是被打包在
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[容器镜像](/examples/service/access/Dockerfile) 里的。
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更好的方法是使用
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[ConfigMap](/zh/docs/tasks/configure-pod-container/configure-pod-configmap/)，
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这样的话你可以更轻易地更改配置。
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{{< /note >}}
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<!--
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## Interact with the frontend Service
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Once you've created a Service of type LoadBalancer, you can use this
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command to find the external IP:
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-->
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### 与前端 Service 交互 {#interact-with-the-frontend-service}
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一旦你创建了 LoadBalancer 类型的 Service，你可以使用这条命令查看外部 IP：
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```shell
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kubectl get service frontend
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```
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<!--
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This displays the configuration for the `frontend` Service and watches for
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changes. Initially, the external IP is listed as `<pending>`:
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-->
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外部 IP 字段的生成可能需要一些时间。如果是这种情况，外部 IP 会显示为 `<pending>`。
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```
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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frontend 10.51.252.116 <pending> 80/TCP 10s
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```
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<!--
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As soon as an external IP is provisioned, however, the configuration updates
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to include the new IP under the `EXTERNAL-IP` heading:
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-->
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当外部 IP 地址被分配可用时，配置会更新，在 `EXTERNAL-IP` 头部下显示新的 IP：
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```
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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frontend 10.51.252.116 XXX.XXX.XXX.XXX 80/TCP 1m
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```
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<!--
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That IP can now be used to interact with the `frontend` service from outside the
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cluster.
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-->
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这一新的 IP 地址就可以用来从集群外与 `frontend` 服务交互了。
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<!--
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## Send traffic through the frontend
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The frontend and backend are now connected. You can hit the endpoint
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by using the curl command on the external IP of your frontend Service.
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-->
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### 通过前端发送流量
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前端和后端已经完成连接了。你可以使用 curl 命令通过你的前端 Service 的外部
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IP 访问服务端点。
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```shell
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curl http://${EXTERNAL_IP} # 将 EXTERNAL_P 替换为你之前看到的外部 IP
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```
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<!--
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The output shows the message generated by the backend:
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-->
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输出显示后端生成的消息：
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```json
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{"message":"Hello"}
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```
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## {{% heading "cleanup" %}}
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<!--
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To delete the Services, enter this command:
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-->
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要删除服务，输入下面的命令：
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```shell
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kubectl delete services frontend backend
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```
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<!--
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To delete the Deployments, the ReplicaSets and the Pods that are running the backend and frontend applications, enter this command:
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-->
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要删除在前端和后端应用中运行的 Deployment、ReplicaSet 和 Pod，输入下面的命令：
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```shell
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kubectl delete deployment frontend backend
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```
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## {{% heading "whatsnext" %}}
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<!--
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* Learn more about [Services](/docs/concepts/services-networking/service/)
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* Learn more about [ConfigMaps](/docs/tasks/configure-pod-container/configure-pod-configmap/)
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* Learn more about [DNS for Service and Pods](/docs/concepts/services-networking/dns-pod-service/)
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-->
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* 进一步了解 [Service](/zh/docs/concepts/services-networking/service/)
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* 进一步了解 [ConfigMap](/zh/docs/tasks/configure-pod-container/configure-pod-configmap/)
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* 进一步了解 [Service 和 Pods 的 DNS](/zh/docs/concepts/services-networking/dns-pod-service/)
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