Here is an example of using ConfigMaps:

# cat configmap/2-7-4_configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: config-example
data:
  app.properties: |
    name=kubernetes-cookbook
    port=443

// create configmap
# kubectl create -f configmap/2-7-4_configmap.yaml
configmap "config-example" created

Similar to Secret, ConfigMaps can be retrieved with environment variables or volumes:

# cat configmap/2-7-4_env.yaml
apiVersion: v1
kind: Pod
metadata:
  name: configmap-env
spec:
  containers:
    - name: configmap
      image: ubuntu
      command: ["/bin/sh", "-c", "while : ;do echo $APP_NAME; sleep 10; done"]
      env:
        - name: APP_NAME
          valueFrom:
            configMapKeyRef:
              name: config-example
              key: app.properties

// create the pod
#kubectl create -f configmap/2-7-4_env.yaml
pod "configmap-env" created

Alternatively, you can use ConfigMaps volume to retrieve the configuration information:

// using configmap in a pod
# cat configmap/2-7-4_volumes.yaml
apiVersion: v1
kind: Pod
metadata:
  name: configmap-volume
spec:
  containers:
    - name: configmap
      image: ubuntu
      command: ["/bin/sh", "-c", "while : ;do cat /src/app/config/app.properties; sleep 10; done"]
      volumeMounts:
      - name: config-volume
        mountPath: /src/app/config
  volumes:
    - name: config-volume
      configMap:
        name: config-example