I have a directory that is configured to be managed by an automounter (as described here). I need to use this directory (and all directories that are mounted inside) in multiple pods as a Local Persistent Volume.
I am able to trigger the automounter within the containers, but there are some use-cases when this directory is not empty when the container starts up. This makes sub-directories appear as empty and not being able to trigger the automounter (whithin the container)
I did some investigation and discovered that when using Local PVs, there is a mount -o bind command between the source directory and some internal directory managed by the kubelet (this is the line in the source code).
What I actually do need is rbind to be used (recursive binding - here is a good explanation).
Using rbind also requires some changes to the part that unmounts the volume (recursive unmounting is needed)
I don't want to patch the kubelet and recompile it..yet. So my question is: are there some official methods to provide to Kubernetes some custom mounter/unmounter?
Meanwhile, I did find a solution for this use-case.
Based on Kubernetes docs there is something called Out-Of-Tree Volume Plugins
The Out-of-tree volume plugins include the Container Storage Interface (CSI) and FlexVolume. They enable storage vendors to create custom storage plugins without adding them to the Kubernetes repository
Even that CSI is encouraged to be used, I chose FlexVolume to implement my custom driver. Here is a detailed documentation.
This driver is actually a py script that supports three actions: init/mount/unmount (--rbind is used to mount that directory managed by automounter and unmounts it like this). It is deployed using a DaemonSet (docs here)
And this is it!