# Define Environment Variables for a Container

Define Environment Variables for a ContainerThis page shows how to define environment variables for a container in a Kubernetes Pod.Before you beginYou 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:iximiuz LabsKillercodaKodeKloudPlay with KubernetesDefine an environment variable for a containerWhen 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.The env and envFrom fields have different effects.envallows you to set environment variables for a container, specifying a value directly for each variable that you name.envFromallows 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.You can read more about ConfigMap 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 "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/hello-app:2.0 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 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.Using environment variables inside of your configEnvironment 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 GREETING, HONORIFIC, and 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 env-print-demo container.Environment variable names may consist of any printable ASCII characters except '='.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.What's nextLearn more about environment variables.Learn about using secrets as environment variables.See EnvVarSource.