Environment Variables

As most applications tend to follow the 12 factor config standard, setting environment variables becomes important to configure the applications. In K8s,there is 3 ways of setting them

Environment Variables in pod spec

As part of the pod definition, one can set environment variables that will be made available inside the container (similar to using the -e flag in docker):

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 80
      env:
        - name: APP_COLOR
          value: blue
        - name: APP_MODE
          value: prod

ConfigMap

ConfigMap objects can be mounted as environment variables for containers. There are two options:

Import all values from the ConfigMap

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 80
      envFrom:
        - configMapRef:
            name: myconfigmap

Import certain values

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 80
      env:
        - name: APP_COLOR
          valueFrom:
            configMapRef:
                name: myconfigmap
                key: color

Secrets

Secret objects can be mounted as environment variables for containers. There are two options:

Import all values from the Secret

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 80
      envFrom:
        - secretRef:
            name: mysecret

Import certain values

apiVersion: v1
kind: Pod
metadata:
  name: simple-webapp-color
spec:
  containers:
    - name: simple-webapp-color
      image: simple-webapp-color
      ports:
        - containerPort: 80
      env:
        - name: APP_COLOR
          valueFrom:
            secretKeyRef:
                name: my-secret
                key: color