Configure Environment Variables in Applications

In this article, we'll explore how to configure environment variables for applications deployed with Kubernetes. First, we review a basic Docker example that establishes an environment variable, then we demonstrate how to specify environment variables directly within a Kubernetes pod manifest. This guide is essential for developers looking to streamline container configuration and deployment.

Setting Environment Variables Using Docker

When running a Docker container, you can set environment variables using the -e flag. For example, the command below sets the APP_COLOR environment variable to "pink":

docker run -e APP_COLOR=pink simple-webapp-color

This command assigns the value "pink" to APP_COLOR while launching the simple-webapp-color container.

Configuring Environment Variables in Kubernetes Pods

Kubernetes allows you to define environment variables within your pod definitions. In the pod manifest, environment variables are listed under the env property, which is an array. Each entry in the array should specify:

• name: The name of the environment variable.
• value: The corresponding value assigned to that environment variable.

Below is an example pod definition that explicitly sets the environment variable:

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 8080
      env:
        - name: APP_COLOR
          value: pink

In this configuration, the container running the simple-webapp-color image will have APP_COLOR set to "pink".

Leveraging ConfigMaps and Secrets for Environment Variables

Instead of hardcoding values into your pod manifest, you can enhance flexibility and security by referencing external configuration sources such as ConfigMaps or Secrets. This approach simplifies maintenance and helps protect sensitive information.

To define an environment variable directly, use:

env:
  - name: APP_COLOR
    value: pink

To reference a ConfigMap for the environment variable, update the definition as follows:

env:
  - name: APP_COLOR
    valueFrom:
      configMapKeyRef:
        name: app-config
        key: color

Similarly, to source the environment variable from a Secret, configure it like this:

env:
  - name: APP_COLOR
    valueFrom:
      secretKeyRef:
        name: app-secrets
        key: color

In both cases, Kubernetes retrieves the value for APP_COLOR from the specified external resource.

Summary

In this article, we covered:

• How to set environment variables using a Docker command.
• Defining environment variables within Kubernetes pod definitions.
• The benefits of leveraging ConfigMaps and Secrets for managing environment configurations.

For additional details and best practices, visit Kubernetes Basics.

That concludes this guide. In our next article, we will explore more advanced Kubernetes configuration techniques, further enhancing your container orchestration capabilities.