[SOLVED] Kubernetes - mount read only share as writable

Kubernetes - mount read only share as writable

I am using this config to mount drive that is read-only to docker image:

volumes:
  - name: drive-c
    hostPath:
      path: /media/sf_C_DRIVE
containers:
  ...
    volumeMounts:
    - name: drive-c
      mountPath: /c

When I try to write (mkdir) to this folder (which is virtual-box read only mounted folder) inside docker image, I get:

mkdir: can't create directory 'somedir': Read-only file system

Which is OK since this is read-only filesystem (C_DRIVE on /c type vboxsf (rw,nodev,relatime))

Is it possible to somehow make this folder writable inside docker container? Changes does not need to be propagated to hostPath. I read something about overlayfs, but I'm not sure how to specify this in Kubernetes yaml.

Solution

You can't do this via Kubernetes volume mounts, as they simply work on volumes. What you need to do is create a writable overlay filesystem on your host machine, then map that into Kubernetes with a different path that is writable.

You want to create something like /mnt/writable_sf_C_drive by mounting your /media/sf_C_DRIVE with an overlay on top of it, then your volume mount in Kubernetes would mount /mnt/writable_sf_C_DRIVE.

There are some instructions here