07 - ConfigMap.md

Playbook Part 7: ConfigMap

A configMap is simple a Kubernetes Object that stores configuration data in a key-value format. This configuration data can then be used to configure software running in a container, by referencing the ConfigMap in the Pod spec.

To check the configmap by using the following command :

  kubectl get configmap

You can also use Yaml descriptor to define configmap :

  apiVersion: v1
  kind: ConfigMap
  metadata:
    name: melon-configmap
  data:
    myKey: myValue
    myFav: myHome

To pass that data to pod.

Play 1 : Mount as environment variable

Create a pod to use configmap data by using environment variables.

apiVersion: v1
kind: Pod
metadata:
  name: melon-configmap
spec:
  containers:
  - name: melonapp-container
    image: busybox
    command: ['sh', '-c', "echo $(MY_VAR) && sleep 3600"]
    env:
    - name: MY_VAR
      valueFrom:
        configMapKeyRef:
          name: my-config-map
          key: myKey

You can use the following command to check the configmap value :

kubectl logs melon-configmap

The output is similar like the following :

Play 2 : Using mounted volume

Create a pod to use configmap data by mounting a data volume.

apiVersion: v1
kind: Pod
metadata:
  name: melon-volume-pod
spec:
  containers:
   - name: myapp-container
     image: busybox
     command: ['sh', '-c', "echo $(cat /etc/config/myKey) && sleep 3600"]
     volumeMounts:
       - name: config-volume
         mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: melon-configmap

You can use the following command to check it as we did for play 1 :

kubectl logs melon-volume-pod

Using the following command to check the config map :

kubectl exec melon-volume-pod -- ls /etc/config

The similar output will look like the following :

You can use the following command to check it exactly :

kubectl exec my-configmap-volume-pod -- cat /etc/config/myKey

Myself also enjoyed to create the configmap from file such as the following ( here k is the alias for kubectl ):

k create configmap fluentd-config --from-file=/usr/test/fluent.conf

k get configmap -o yaml > config.yaml