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Define Environment Variables for a Container

This page shows how to define environment variables when you run a container in a Kubernetes Pod.

• Before you begin
• Define an environment variable for a container
• What’s next

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

• Katacoda
• Play with Kubernetes

To check the version, enter kubectl version.

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 file for the Pod:

envars.yaml
apiVersion: v1 kind: Pod metadata: name: envar-demo labels: purpose: demonstrate-envars spec: containers: - name: envar-demo-container image: gcr.io/google-samples/node-hello:1.0 env: - name: DEMO_GREETING value: "Hello from the environment" - name: DEMO_FAREWELL value: "Such a sweet sorrow"

1. Create a Pod based on the YAML configuration file:

   kubectl create -f https://k8s.io/docs/tasks/inject-data-application/envars.yaml
   

2. List the running Pods:

   kubectl get pods -l purpose=demonstrate-envars
   

   The output is similar to this:

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

3. Get a shell to the container running in your Pod:

   kubectl exec -it envar-demo -- /bin/bash
   

4. In your shell, run the printenv command to list the environment variables.

   root@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
   

5. To exit the shell, enter exit.

Note: The environment variables set using the env or envFrom field will override any environment variables specified in the container image.

What’s next

• Learn more about environment variables.
• Learn about using secrets as environment variables.
• See EnvVarSource.