Persistent volume claim subPath initializer

Michael Grant, Anaconda, Inc., November 2021

Motivation

StackOverflow background here.

When a Kubernetes pod mounts a PVC with a non-empty subPath, it will create that subdirectory on the volume if it does not yet exist. Unfortunately, the resulting ownership and permissions are often not what the downstream container can accept. This script is designed to run within an initContainer given the same volumeMount, but without the subpath. It can then create the subdirectory and ensure that it has the proper permissions.

Example

Consider this volumeMount:

- name: test-mount
  mountPath: /mount/point
  subPath: sub/path

An initContainer might look like this:

- name: storage-permissions
  image: <IMAGE_NAME>
  volumeMounts:
  - name: test-mount
    mountPath: /mount/point
  command: ["/init_dir.sh", "/mount/point", "sub/path"]

The image itself can be virtually any image; typically you would re-use the pod's container image. The output looks something like this:

----------------------
Mount path: /mount/path
Full path: /mount/path/sub/path
----------------------
- Attempting to create /mount/path/sub/path
> mkdir -p /mount/path/sub/path
> ls -ld /mount/path/sub/path
| drwxr-xr-x 2 1002 23456 4096 Dec  3 15:54 /mount/path/sub/path
- Permissions: 755
- Setting directory permissions with setgid
> chmod 2775 /persistence-v/persistence/projects
- New permissions: 2775
> ls -ld /persistence-v/persistence/projects
| drwxrwsr-x 2 1002 23456 4096 Dec  3 15:54 ls -ld /mount/path/sub/path
- Testing writability
> touch /mount/path/sub/path/.test_write
> rm /mount/path/sub/path/.test_write
----------------------

Public domain / no warranty

This entire repository has been released to the public domain; or more precisely, the CC0 1.0 Universal license.

Please feel free to use this in any context, modified in any way you choose, without attribution.

That said, this work is also entirely unsupported and comes with no warranty. It works for me, and I do hope it works for you!