You can do this the normal way which will take some time. This says experimental Python script to quickly setup an immutable repository but works very well
I never used it. But I heard good feedback from other customers.
Please note, we released a new hardening script two weeks ago. Please have a look. https://www.veeam.com/sys507
This did not work for some reason Installable .ISO but I manually installed Ubuntu core, did the patching/harden, Format 2nd drive XFS, set permission etc.. & it worked
(Just like Rick's post https://www.youtube.com/watch?v=e2SFMixp92g)