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Define Environment Variables for a Container

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

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:

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:

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 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. 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.

    # Run this in the shell inside the container
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 override any environment variables specified in the container image.
Note: The environment variables can reference each other, and cycles are possible, pay attention to the order before using

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.

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