How to proberly share a directory between two containers?

Hi there!
I tried to find a solution for the following setup:

A folder on a external hdd should be shared between to containers. Both should have rw permissions. Plus: In container B www-data should also have rw permissions to the folder.

What would be the best solution for that?

Is this for LXC or LXD?

Lxd 5.6 :+1: