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Kubernetes: 20. ConfigMaps

 A Java map is a object that maps key to value. The key has to be unique.

Environment Variables
  • Environment variables can be directly added into Pod definition file under specs.env array
  • But they will be limited to only the pod for which they are added
  • For new Pods, the environment variables have to be added again
ConfigMaps
  • ConfigMaps are a way of storing the data in key: value pair
  • This data is then injected into Pods via the definition file
  • The data injected can be created as environment variables in the pod
  • Or the data is just injected as a file that then can be used by the pod
Create ConfigMaps
There are two ways to create the ConfigMaps like any other Kubernetes objects
  1. Imperative 
  2. Declarative
    • Note that in the declarative way there is no specs, we instead have data section
config-map
APP_COLOR: Blue
APP_ENV: Prod

config-map-creation-imperative
kubectl create configmap
-> Imperative way of creating configmap

<config-name> --from-literal=<key>=<value>
-> Add key value pairs by mentioning from-literal

kubectl create configmap
-> Imperative way of creating configmap

<config-name> --from-file=<path-to-file>
-> Add key value pairs by passing through a file by mentioning from-file

kubectl create configmap \
<config-name> --from-literal=APP_COLOR=Blue \
--from-literal=APP_ENV=Prod \

kubectl create configmap \
<config-name> --from-file=app_config.properties

config-map-creation-declarative.yaml
apiVersion: v1
kind: ConfigMap
metadata:
    name: app-config

data:
    APP_COLOR=Blue
    APP_ENV=Prod

kubectl create -f config-map-definition.yaml
-> Create the configmap

kubectl get configmaps
-> Get all the configmaps in the existing namespace

kubectl describe configmaps
-> Describe all the configmaps in the existing namespace

kubectl describe configmaps <config-map-name>
-> Describe the configmap <config-map-name> in the existing namespace

Add ConfigMaps to the Pods
  • ConfigMaps can be added in variety of ways to the pods
  • The entire ConfigMap references can be injected into the pod
  • This can be seen from below spec.envFrom.configMapRef array
    • Here we provide the name of the configMapRef
    • Since this is an array, you can inject multiple configMaps
  • Only a single value from ConfigMap can be injected
  • This can be seen from spec.env array
    • Here we provide the name of our variable
    • Value is taken from a ConfigMap, with the name of the ConfigMap and the key name provided
    • Since this is any array, you can inject multiple variables
  • ConfigMap can be injected as a file by using volumes
  • This can be seen from spec.volumes
    • Name of the configMap that has to be injected into the Pod is provided
    • ConfigMap is then mounted as a file on the pod
pod-definition.yaml
apiVersion: v1
kind: Pod
metadata:
    name: my-color-webapp

spec:
    containers:
    - name: my-color-container
      image: simple-webapp-color
      ports:
      - containerPort: 8080
      envFrom:
      - configMapRef:
            name: app-config

      env:
      - name: APP_COLOR
        valueFrom:
            configMapKeyRef:
                name: app-config
                key: APP_COLOR

      volumes:
      - name: app-config-volume
        configMap:
            name: app-config

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