How to merge two configmaps using volume mount in kubernetes

Question

I am having two different config maps test-configmap and common-config. I tried to mount them at the same location, but one config map overwrote the other. Then I read about subPath and did not work.

deploy.yaml

apiVersion: apps/v1beta1 # for versions before 1.8.0 use apps/v1beta1
kind: Deployment
metadata:
  name: testing
spec:
  replicas: 1
  template:
    metadata:
      name: testing
      labels:
        app: testing
    spec:
      containers:
      - name: testing-container
        image: testing
        imagePullPolicy: IfNotPresent
      ports:
      - containerPort: __PORT__
      volumeMounts:
      - name: commonconfig-volume
        mountPath: /usr/src/app/config/test.config
        subPath: test.config
    volumes:
      - name: commonconfig-volume
        configMap:
          name: test-configmap
      - name: commonconfig-volume
        configMap:
          name: common-config

Error :

The Deployment "testing" is invalid: spec.template.spec.volumes[1].name: Duplicate value: "commonconfig-volume"

I am not sure if merging two config map achievable of not. And if yes then how should I do it.

Answer 1

You have to use special projected volumes for achieve that. Example your deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: testing
spec:
  replicas: 1
  selector:
    matchLabels:
      app: testing
  template:
    metadata:
      name: testing
      labels:
        app: testing
    spec:
      containers:
      - name: testing-container
        image: testing
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: __PORT__
        volumeMounts:
        - name: commonconfig-volume
          mountPath: /usr/src/app/config
      volumes:
        - name: commonconfig-volume
          projected:
            sources:
            - configMap:
                name: test-configmap
            - configMap:
                name: common-config

You can use secret same as configMap