• In previous lectures, we saw how to define environment variables in pod definition files.
  • ConfigMaps take that information out of the pod definition file and manage it centrally.
  • ConfigMaps take configuration data in the form of key:value pairs. An example is below: 
    APP_COLOR: blue
APP_MODE: prod
  • You then add the ConfigMap into the pod definition file to how the variables there.
  • Example pod definition file: ``` apiVersion: v1 kind: `pd metadata: name: simple-webapp-color spec: containers:
    • name: simple-webapp-container image: simple-webapp-container ports:
      • containerPort:

      envFrom:

      • configMapRef: name: app-contents ```
  • Phases for creating ConfigMaps:
    • Create the ConfigMap.
    • Inject it into the pod.
  • To create a ConfigMap in the imperative way, run the below command: 
    kubectl create configmap
  • Or the declerative way by using a ConfigMap definition file: 
    kubectl create -f
  • Imperative way option 1): 
    kubectl create configmap <config-name> --from-literal=<key>=<value>
  • Imperative way option 2): 
    kubectl create configmap \
  app-config --from-literal=APP_COLOR=blue
  • The option --from-literal - used to specify the key:value pairs within the command itself.
  • If you wish to add multiple key:value pairs, add the --from-literal option multiple times: 
    kubectl create configmap \
  app-config --from-literal=APP_COLOR=blue --from-literal=APP_MODE=prod
  • Imperative way option 3): through a file: 
    kubectl create configmap
 <config-name> --from-file=<path-to-file>

    kubectl create configmap \
  app-config --from-file=app_config.properties
  • The declerative approach looks like this: 
    kubectl create -f
  • Example ConfigMap yaml file: 
    apiVersion: v1
kind: ConfigMap
metadata:
name: app-config
data:
APP_COLOR: blue
APP_MODE: prod
  • kubectl create -f ConfigMap
  • Map sure to rename multiple different ConfigMaps correctly for different applications. Example ConfigMaps are below: app-config 
    APP_COLOR: blue
APP_MODE: prod

    mysql-config

    port: 3306
max_allowed_packet: 128M

    redis-config

    port: 6379
rdb-compression: yes
  • To view ConfigMaps, run: 
    kubectl get configmaps
  • Describe a ConfigMap with: 
    kubectl describe configmaps
  • Configuration data is listed under the DATA section.
  • Example pod definition file: ``` apiVersion: v1 kind: Pod metadata: name: simple-webapp-color spec: containers:
    • name: simple-webapp-color image: simple-webapp-color ports:
      • containerPort: 8080

      envFrom:

      • configMapRef: name: app-contents ```
  • The ConfigMap we are pairing this with is: 
    apiVersion: v1
kind: ConfigMap
metadata:
name: app-config
data:
APP_COLOR: blue
APP_MODE: prod
  • Creating the above pod from the pod definition file creates an application with a blue background.
  • There are other ways to inject environment variables into pods: ``` envFrom:
    • configMapRef: name: app-config ```
  • For single environment variables: ``` env:
    • name: APP_COLOR valueFrom: configMapKeyRef: name: app-config key: APP_COLOR ```
  • Also as files in a volume: ``` volumes:
  • name: app-config-volume configMap: name: app-config ```

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