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

title	content_type	weight
Define Dependent Environment Variables	task	20

This page shows how to define dependent environment variables for a container in a Kubernetes Pod.

{{% heading "prerequisites" %}}

{{< include "task-tutorial-prereqs.md" >}}

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:

{{< codenew file="pods/inject/dependent-envars.yaml" >}}

1. Create a Pod based on that manifest:

   kubectl apply -f https://k8s.io/examples/pods/inject/dependent-envars.yaml
   

   pod/dependent-envars-demo created
   

2. List the running Pods:

   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:

   kubectl logs pod/dependent-envars-demo
   

   SERVICE_ADDRESS
   https://172.17.0.1:80
   UNCHANGED_REFERENCE
   $(PROTOCOL)://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 the environment variable is defined, you can use it directly. You can use it after the definition is completed, such as SERVICE_ADDRESS.

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. A bad reference does not interfere with the operation of the container.

The (VAR_NAME) syntax can be escaped with a double , ie: $(VAR_NAME).Escaped references will never be expanded, regardless of whether the variable exists or not.

{{% heading "whatsnext" %}}

• Learn more about environment variables.
• See [EnvVarSource](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#envvarsource-v1-core).