08-Configure-ConfigMaps-in-Applications.md

Configure ConfigMaps in Applications

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In this section, we will take a look at configuring configmaps in applications

ConfigMaps

• There are 2 phases involved in configuring ConfigMaps.
  • First, create the configMaps
  • Second, Inject then into the pod.
• There are 2 ways of creating a configmap.

  • The Imperative way

    $ kubectl create configmap app-config --from-literal=APP_COLOR=blue --from-literal=APP_MODE=prod
    $ kubectl create configmap app-config --from-file=app_config.properties (Another way)
    

    

  • The Declarative way

    apiVersion: v1
    kind: ConfigMap
    metadata:
     name: app-config
    data:
     APP_COLOR: blue
     APP_MODE: prod
    

    Create a config map definition file and run the 'kubectl create` command to deploy it.
    $ kubectl create -f config-map.yaml
    

    

View ConfigMaps

• To view configMaps

  $ kubectl get configmaps (or)
  $ kubectl get cm
  

• To describe configmaps

  $ kubectl describe configmaps
  

  

ConfigMap in Pods

• Inject configmap in pod

  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-config
  

  apiVersion: v1
  kind: ConfigMap
  metadata:
    name: app-config
  data:
    APP_COLOR: blue
    APP_MODE: prod
  

  $ kubectl create -f pod-definition.yaml
  

  

There are other ways to inject configuration variables into pod

• You can inject it as a Single Environment Variable

• You can inject it as a file in a Volume

  

K8s Reference Docs

• https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/
• https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#define-container-environment-variables-using-configmap-data
• https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#create-configmaps-from-files