Passing Environment Variables to Kubernetes Pods

To pass environment variables to Kubernetes Pods, you can define them directly in your Pod or Deployment manifest, or pull them from external resources like ConfigMaps and Secrets.

1. Direct Definition

Use the env field within your container specification to define key-value pairs directly.

yaml
spec:
  containers:
  - name: my-container
    image: nginx
    env:
    - name: APP_COLOR
      value: "blue"

2. Using ConfigMaps (Non-Sensitive Data)

ConfigMaps allow you to decouple configuration from your image.

• Single Key: Use valueFrom and configMapKeyRef.
• All Keys: Use envFrom to inject every key in a ConfigMap as an environment variable.

yaml
envFrom:
- configMapRef:
    name: my-configmap

3. Using Secrets (Sensitive Data)

For passwords or API keys, use Secrets. This works similarly to ConfigMaps but provides a layer of security for sensitive data.

yaml
env:
- name: DB_PASSWORD
  valueFrom:
    secretKeyRef:
      name: my-secret
      key: password

4. Injecting Pod/Node Metadata (Downward API)

You can expose Pod information (like its IP address or the Node name it's running on) as environment variables using fieldRef.

yaml
env:
- name: MY_POD_IP
  valueFrom:
    fieldRef:
      fieldPath: status.podIP

5. Using Command Line (kubectl)

You can quickly update environment variables for an existing Deployment or ReplicaSet without editing the YAML file manually.

• Set variable: kubectl set env deployment/my-deploy APP_ENV=prod
• Remove variable: kubectl set env deployment/my-deploy APP_ENV-

Summary of Methods

Method	Best For	Reference Field
Direct	Simple, static values	env
ConfigMap	Non-sensitive app config	configMapKeyRef or envFrom
Secret	Credentials/Tokens	secretKeyRef or envFrom
Downward API	Pod/Node metadata	fieldRef