Skip to content

Config Map

https://kubernetes.io/docs/concepts/configuration/configmap/#using-configmaps-as-environment-variables

Environment Variables

Pods are disposable and do not retain persistent changes.

We can inject environment variables into a Pod at runtime.

Example

apiVersion: v1
kind: Pod
metadata:
  name: env-configmap
spec:
  containers:
  - name: envars-test-container
    image: nginx
    env:
    - name: CONFIGMAP_USERNAME
      valueFrom:
        configMapKeyRef:
          name: myconfigmap
          key: username

Create Config Maps - Imperative

https://kubernetes.io/docs/reference/kubectl/generated/kubectl_create/kubectl_create_configmap/

kubectl create configmap db-config --from-literal=MYSQL_DATABASE=accounts \
 --from-literal=MYSQL_ROOT_PASSWORD=somecomplexpass

configmap/db-config created


kubectl get cm

kubectl get cm db-config -o yaml

kubectl describe cm db-config

Create Config Maps - Declarative

apiVersion: v1
kind: ConfigMap
metadata:
  name: db-config
data:
  MYSQL_ROOT_PASSWORD: somecomplexpass
  MYSQL_DATABASE: accounts

Apply changes: 

kubectl create -f db-cm.yml

POD Reading Config Maps

apiVersion: v1
kind: Pod
metadata:
  name: db-pod
  labels:
    app: db
    project: infinity
spec:
  containers:
    - name: mysql-container
      image: mysql:5.7
      envFrom:
        - configMapRef:
            name: db-config
      ports:
        - name: db-port
          containerPort: 3306

Select a Key from a Config Map

apiVersion: v1
kind: Pod
metadata:
  name: db-pod
  labels:
    app: db
    project: infinity
spec:
  containers:
    - name: mysql-container
      image: mysql:5.7
      env:
        - name: DB_HOST
          valueFrom:
            configMapKeyRef:
              name: db-config
              key: DB_HOST
      ports:
        - name: db-port
          containerPort: 3306

Hands On

vim samplecm.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: game-demo
data:
  # property-like keys; each key maps to a simple value
  player_initial_lives: "3"
  ui_properties_file_name: "user-interface.properties"

  # file-like keys
  game.properties: |
    enemy.types=aliens,monsters
    player.maximum-lives=5    
  user-interface.properties: |
    color.good=purple
    color.bad=yellow
    allow.textmode=true

kubectl apply -f samplecm.yaml

kubectl get cm

kubectl get cm game-demo -o yaml

There are four different ways that you can use a ConfigMap to configure a container inside a Pod:

  1. Inside a container command and args
  2. Environment variables for a container
  3. Add a file in read-only volume, for the application to read
  4. Write code to run inside the Pod that uses the Kubernetes API to read a ConfigMap
vim readcmpod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: configmap-demo-pod
spec:
  containers:
    - name: demo
      image: alpine
      command: ["sleep", "3600"]
      env:
        # Define the environment variable
        - name: PLAYER_INITIAL_LIVES # Notice that the case is different here
                                     # from the key name in the ConfigMap.
          valueFrom:
            configMapKeyRef:
              name: game-demo           # The ConfigMap this value comes from.
              key: player_initial_lives # The key to fetch.
        - name: UI_PROPERTIES_FILE_NAME
          valueFrom:
            configMapKeyRef:
              name: game-demo
              key: ui_properties_file_name
      volumeMounts:
      - name: config
        mountPath: "/config"
        readOnly: true
  volumes:
  # You set volumes at the Pod level, then mount them into containers inside that Pod
  - name: config
    configMap:
      # Provide the name of the ConfigMap you want to mount.
      name: game-demo
      # An array of keys from the ConfigMap to create as files
      items:
      - key: "game.properties"
        path: "game.properties"
      - key: "user-interface.properties"
        path: "user-interface.properties"

kubectl get cm

kubectl apply -f readcmpod.yaml

kubectl get pod

kubectl exec --stdin --tty configmap-demo-pod -- /bin/sh

Validate 

ls /config/


cat /config/game.properties

cat /config/user-interface.properties

echo $PLAYER_INITIAL_LIVES

echo $UI_PROPERTIES_FILE_NAME