Define Environment Variables for a Container

    You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using or you can use one of these Kubernetes playgrounds:

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

    The env and envFrom fields have different effects.

    env

    allows you to set environment variables for a container, specifying a value directly for each variable that you name.

    envFrom

    You can read more about and Secret.

    This page explains how to use env.

    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 . Here is the configuration manifest for the Pod:

    1. List the running Pods:

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

    2. List the Pod’s container environment variables:

      The output is similar to this:

      1. NODE_VERSION=4.4.2
      2. HOSTNAME=envar-demo
      3. ...
      4. DEMO_GREETING=Hello from the environment

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

    Note: Environment variables may reference each other, however ordering is important. Variables making use of others defined in the same context must come later in the list. Similarly, avoid circular references.

    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 container.

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