I am chasing down how the "preinstalled" Raspberry Pi images are being generated. What I found so far:
ubuntu-image is the tool for generating those images, which requires a yaml file with the definition of the image to build. Unfortunately I haven't been able to find the source for the build. In the models repo, the preinstalled one is missing.
I just want to be able to pre-bake images so it can be pre-provisioned to the iSCSI servers automatically. It is very interesting that in an opensource world, this particular piece is terribly hidden.
It seems that there are some unit tests that contain files that should be close to what preinstall is doing on "internal/statemachine/testdata/image_definitions/test_raspi.yaml" in the ubuntu-image repository.
There are multiple places where this is being asked such as here, here, and here.
