kubernetes mount file on an existing folder

With ConfigMap and Secret you can "populate" a volume with files and "mount" that volume to a container, so that the application can access those files.


echo "one=1"> file1.properties
echo "two=2"> file2.properties
kubectl create configmap myconfig --from-file file1.properties --from-file file2.properties
kubectl describe configmaps myconfig

Name:         myconfig
Namespace:    default
Labels:       
Annotations:  

Data
====
file1.properties:
----
one=1

file2.properties:
----
two=2

Events:  

Now I can mount the ConfigMap into a Pod, as described here


cat mypod.yml

apiVersion: v1
kind: Pod
metadata:
  name: configmap-pod
spec:
  containers:
    - name: test
      image: nginx
      volumeMounts:
        - name: config-vol
          mountPath: /etc/config
  volumes:
    - name: config-vol
      configMap:
        name: myconfig
        items:
          - key: file1.properties
            path: myfile1.properties

kubectl create -f mypod.yml

kubectl exec -ti configmap-pod bash

cat /etc/config/myfile1.properties
one=1




Now I change the image to vernetto/mynginx, which contains already a /etc/config/file0.properties
The existing folder /etc/config/ is completely replaced by the volumeMount, so file0.properties disappears!
Only /etc/config/file1.properties is there.

They claim that one can selectively mount only one file from the volume, and leave the original files in the base image:
https://stackoverflow.com/questions/33415913/whats-the-best-way-to-share-mount-one-file-into-a-pod/43404857#43404857 using subPath, but it is definitely not working for me.