if there are some custom image, e.g. additional stuff I added to an existing image, then I backup the dockerfile. you can rebuild the image anytime and the size is smaller than a binary.

if you just want to have a solution where you can create / delete multiple local dns records on a raspberry, you van use terraform, it has a raspberry provider. I tried it recently, i was able to import existing records, create new ones. you just have to keep the list in a terraform project.

if you want to self host and not open to the internet, alpinelinux is small, install docker and run your containert there, low footprint.