This page shows how to define environment variables for a container in a Kubernetes Pod.
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 minikube 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 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:
pods/inject/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"
Create a Pod based on that manifest:
kubectl apply -f https://k8s.io/examples/pods/inject/envars.yaml
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
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
env
or envFrom
field override any environment variables specified in the container image. 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.
© 2022 The Kubernetes Authors
Documentation Distributed under CC BY 4.0.
https://kubernetes.io/docs/tasks/inject-data-application/define-environment-variable-container/