117 lines
3.3 KiB
Markdown
117 lines
3.3 KiB
Markdown
---
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title: Define Environment Variables for a Container
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content_type: task
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weight: 20
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---
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<!-- overview -->
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This page shows how to define environment variables for a container
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in a Kubernetes Pod.
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## {{% heading "prerequisites" %}}
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{{< include "task-tutorial-prereqs.md" >}}
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<!-- steps -->
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## Define an environment variable for a container
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When you create a Pod, you can set environment variables for the containers
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that run in the Pod. To set environment variables, include the `env` or
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`envFrom` field in the configuration file.
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In this exercise, you create a Pod that runs one container. The configuration
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file for the Pod defines an environment variable with name `DEMO_GREETING` and
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value `"Hello from the environment"`. Here is the configuration manifest for the
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Pod:
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{{< codenew file="pods/inject/envars.yaml" >}}
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1. Create a Pod based on that manifest:
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```shell
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kubectl apply -f https://k8s.io/examples/pods/inject/envars.yaml
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```
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1. List the running Pods:
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```shell
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kubectl get pods -l purpose=demonstrate-envars
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```
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The output is similar to:
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```
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NAME READY STATUS RESTARTS AGE
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envar-demo 1/1 Running 0 9s
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```
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1. List the Pod's container environment variables:
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```shell
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kubectl exec envar-demo -- printenv
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```
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The output is similar to this:
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```
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NODE_VERSION=4.4.2
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EXAMPLE_SERVICE_PORT_8080_TCP_ADDR=10.3.245.237
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HOSTNAME=envar-demo
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...
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DEMO_GREETING=Hello from the environment
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DEMO_FAREWELL=Such a sweet sorrow
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```
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{{< note >}}
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The environment variables set using the `env` or `envFrom` field
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override any environment variables specified in the container image.
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{{< /note >}}
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{{< note >}}
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Environment variables may reference each other, however ordering is important.
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Variables making use of others defined in the same context must come later in
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the list. Similarly, avoid circular references.
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{{< /note >}}
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## Using environment variables inside of your config
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Environment variables that you define in a Pod's configuration can be used
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elsewhere in the configuration, for example in commands and arguments that
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you set for the Pod's containers.
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In the example configuration below, the `GREETING`, `HONORIFIC`, and
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`NAME` environment variables are set to `Warm greetings to`, `The Most
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Honorable`, and `Kubernetes`, respectively. Those environment variables
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are then used in the CLI arguments passed to the `env-print-demo`
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container.
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: print-greeting
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spec:
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containers:
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- name: env-print-demo
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image: bash
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env:
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- name: GREETING
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value: "Warm greetings to"
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- name: HONORIFIC
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value: "The Most Honorable"
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- name: NAME
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value: "Kubernetes"
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command: ["echo"]
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args: ["$(GREETING) $(HONORIFIC) $(NAME)"]
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```
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Upon creation, the command `echo Warm greetings to The Most Honorable Kubernetes` is run on the container.
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## {{% heading "whatsnext" %}}
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* Learn more about [environment variables](/docs/tasks/inject-data-application/environment-variable-expose-pod-information/).
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* Learn about [using secrets as environment variables](/docs/concepts/configuration/secret/#using-secrets-as-environment-variables).
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* See [EnvVarSource](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#envvarsource-v1-core).
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