Merge pull request #24159 from zhiguo-lu/zh-addpage-task-define-interdependent-environment-variables

add page: zh-task-define-interdependent-environment-variables, fix #24157

content/zh/docs/tasks/inject-data-application/define-interdependent-environment-variables.md

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+---
+title: 定义相互依赖的环境变量
+content_type: task
+weight: 20
+---
+<!-- 
+title: Define Dependent Environment Variables
+-->
+
+<!-- overview -->
+
+<!-- 
+This page shows how to define dependent environment variables for a container
+in a Kubernetes Pod.
+-->
+本页展示了如何为 Kubernetes Pod 中的容器定义相互依赖的环境变量。
+
+## {{% heading "prerequisites" %}}
+
+
+{{< include "task-tutorial-prereqs.md" >}}
+
+
+<!-- steps -->
+
+<!-- 
+## Define an environment dependent variable for a container
+
+When you create a Pod, you can set dependent environment variables for the containers that run in the Pod. To set dependent environment variables, you can use $(VAR_NAME) in the `value` of `env` in the configuration file.
+
+In this exercise, you create a Pod that runs one container. The configuration
+file for the Pod defines an dependent environment variable with common usage defined. Here is the configuration manifest for the
+Pod:
+-->
+## 为容器定义相互依赖的环境变量   {#define-an-environment-dependent-variable-for-a-container}
+
+当创建一个 Pod 时，你可以为运行在 Pod 中的容器设置相互依赖的环境变量。 
+设置相互依赖的环境变量，你就可以在配置清单文件的 `env` 的 `value` 中使用 $(VAR_NAME)。
+
+在本练习中，你会创建一个单容器的 Pod。
+此 Pod 的配置文件定义了一个已定义常用用法的相互依赖的环境变量。
+下面是 Pod 的配置清单：
+
+{{< codenew file="pods/inject/dependent-envars.yaml" >}}
+
+<!-- 1. Create a Pod based on that manifest: -->
+1. 依据清单创建 Pod：
+    ```shell
+    kubectl apply -f https://k8s.io/examples/pods/inject/dependent-envars.yaml
+    ```
+    ```
+    pod/dependent-envars-demo created
+    ```
+    <!-- 2. List the running Pods: -->
+2. 列出运行的 Pod：
+
+    ```shell
+    kubectl get pods dependent-envars-demo
+    ```
+    ```
+    NAME                      READY     STATUS    RESTARTS   AGE
+    dependent-envars-demo     1/1       Running   0          9s
+    ```
+
+    <!-- 3. Check the logs for the container running in your Pod: -->
+3. 检查 Pod 中运行容器的日志：
+
+    ```shell
+    kubectl logs pod/dependent-envars-demo
+    ```
+    ```
+
+    UNCHANGED_REFERENCE=$(PROTOCOL)://172.17.0.1:80
+    SERVICE_ADDRESS=https://172.17.0.1:80
+    ESCAPED_REFERENCE=$(PROTOCOL)://172.17.0.1:80
+    ```
+
+<!-- 
+As shown above, you have defined the correct dependency reference of `SERVICE_ADDRESS`, bad dependency reference of `UNCHANGED_REFERENCE` and skip dependent references of `ESCAPED_REFERENCE`.
+
+When an environment variable is already defined when being referenced,
+the reference can be correctly resolved, such as in the `SERVICE_ADDRESS` case.
+-->
+如上所示，你已经定义了 `SERVICE_ADDRESS` 的正确依赖引用，
+`UNCHANGED_REFERENCE` 的错误依赖引用，
+并跳过了 `ESCAPED_REFERENCE` 的依赖引用。
+
+如果环境变量被引用时已事先定义，则引用可以正确解析，
+比如 `SERVICE_ADDRESS` 的例子。
+
+<!-- 
+When the environment variable is undefined or only includes some variables, the undefined environment variable is treated as a normal string, such as `UNCHANGED_REFERENCE`. Note that incorrectly parsed environment variables, in general, will not block the container from starting.
+
+The `$(VAR_NAME)` syntax can be escaped with a double `$`, ie: `$$(VAR_NAME)`.
+Escaped references are never expanded, regardless of whether the referenced variable
+is defined or not. This can be seen from the `ESCAPED_REFERENCE` case above.
+-->
+当环境变量未定义或仅包含部分变量时，未定义的变量会被当做普通字符串对待，
+比如 `UNCHANGED_REFERENCE` 的例子。
+注意，解析不正确的环境变量通常不会阻止容器启动。
+
+`$(VAR_NAME)` 这样的语法可以用两个 `$` 转义，既：`$$(VAR_NAME)`。
+无论引用的变量是否定义，转义的引用永远不会展开。
+这一点可以从上面 `ESCAPED_REFERENCE` 的例子得到印证。
+
+## {{% heading "whatsnext" %}}
+
+
+<!--
+* Learn more about [environment variables](/docs/tasks/inject-data-application/environment-variable-expose-pod-information/).
+* See [EnvVarSource](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#envvarsource-v1-core).
+-->
+* 进一步了解[环境变量](/zh/docs/tasks/inject-data-application/environment-variable-expose-pod-information/).
+* 参阅 [EnvVarSource](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#envvarsource-v1-core).
+

content/zh/examples/pods/inject/dependent-envars.yaml

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+apiVersion: v1
+kind: Pod
+metadata:
+  name: dependent-envars-demo
+spec:
+  containers:
+    - name: dependent-envars-demo
+      args:
+        - while true; do echo -en '\n'; printf UNCHANGED_REFERENCE=$UNCHANGED_REFERENCE'\n'; printf SERVICE_ADDRESS=$SERVICE_ADDRESS'\n';printf ESCAPED_REFERENCE=$ESCAPED_REFERENCE'\n'; sleep 30; done;
+      command:
+        - sh
+        - -c
+      image: busybox
+      env:
+        - name: SERVICE_PORT
+          value: "80"
+        - name: SERVICE_IP
+          value: "172.17.0.1"
+        - name: UNCHANGED_REFERENCE
+          value: "$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"
+        - name: PROTOCOL
+          value: "https"
+        - name: SERVICE_ADDRESS
+          value: "$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"
+        - name: ESCAPED_REFERENCE
+          value: "$$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"