website/content/en/docs/tasks/inject-data-application/define-environment-variable-container.md

title	content_type	weight
Define Environment Variables for a Container	task	20

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

{{% heading "prerequisites" %}}

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

Define an environment variable for a container

When you create a Pod, you can set environment variables for the containers that run in the Pod. To set environment variables, include the env or envFrom field in the configuration file.

In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines an environment variable with name DEMO_GREETING and value "Hello from the environment". Here is the configuration manifest for the Pod:

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

1. Create a Pod based on that manifest:

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

2. List the running Pods:

   kubectl get pods -l purpose=demonstrate-envars
   

   The output is similar to:

   NAME            READY     STATUS    RESTARTS   AGE
   envar-demo      1/1       Running   0          9s
   

3. List the Pod's container environment variables:

   kubectl exec envar-demo -- printenv
   

   The output is similar to this:

   NODE_VERSION=4.4.2
   EXAMPLE_SERVICE_PORT_8080_TCP_ADDR=10.3.245.237
   HOSTNAME=envar-demo
   ...
   DEMO_GREETING=Hello from the environment
   DEMO_FAREWELL=Such a sweet sorrow
   

{{< note >}} The environment variables set using the env or envFrom field override any environment variables specified in the container image. {{< /note >}}

{{< note >}} The environment variables can reference each other, and cycles are possible, pay attention to the order before using {{< /note >}}

Using environment variables inside of your config

Environment variables that you define in a Pod's configuration can be used elsewhere in the configuration, for example in commands and arguments that you set for the Pod's containers. In the example configuration below, the GREETING, HONORIFIC, and NAME environment variables are set to Warm greetings to, The Most Honorable, and Kubernetes, respectively. Those environment variables are then used in the CLI arguments passed to the env-print-demo container.

apiVersion: v1
kind: Pod
metadata:
  name: print-greeting
spec:
  containers:
  - name: env-print-demo
    image: bash
    env:
    - name: GREETING
      value: "Warm greetings to"
    - name: HONORIFIC
      value: "The Most Honorable"
    - name: NAME
      value: "Kubernetes"
    command: ["echo"]
    args: ["$(GREETING) $(HONORIFIC) $(NAME)"]

Upon creation, the command echo Warm greetings to The Most Honorable Kubernetes is run on the container.

{{% heading "whatsnext" %}}

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