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. 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:
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
envFrom field in the configuration file.
envFrom fields have different effects.
- allows you to set environment variables for a container, specifying a value directly for each variable that you name.
- allows you to set environment variables for a container by referencing either a ConfigMap or a Secret.
When you use
envFrom, all the key-value pairs in the referenced ConfigMap or Secret are set as environment variables for the container. You can also specify a common prefix string.
This page explains how to use
In this exercise, you create a Pod that runs one container. The configuration
file for the Pod defines an environment variable with name
"Hello from the environment". Here is the configuration manifest for the
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
envFromfield override any environment variables specified in the container image.
Using environment variables inside of your config
Environment variables that you define in a Pod's configuration under
.spec.containers[*].env[*] 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
NAME environment variables are set to
Warm greetings to,
The Most Honorable, and
Kubernetes, respectively. The environment variable
MESSAGE combines the set of all these environment variables and then uses it
as a CLI argument passed to the
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" - name: MESSAGE value: "$(GREETING) $(HONORIFIC) $(NAME)" command: ["echo"] args: ["$(MESSAGE)"]
Upon creation, the command
echo Warm greetings to The Most Honorable Kubernetes is run on the container.