Does it replace Kabuki in non priviledged CI builds? Can one exchange lower / independent layers like with nix container builds?
> Does it replace Kabuki in non priviledged CI builds?
I have never heard of Kabuki, and couldn't find it in a quick web search. Did you mean Kaniko?
> Can one exchange lower / independent layers like with nix container builds?
Yes.
How does that work? Are you building special adaptors that understand how package manager metadata files work? A deb package's postinstall is basically just a blob of bash running as root with access to the whole filesystem. If I tell dagger to install three packages in three different steps, those are not trivially reorderable operations. Nor are they reproducible at all, without Dagger having additional insight into the state of the local apt cache and what is offered by the remote apt repo at the moment of execution.
Yes, Dagger provides the core system API that allows creating and combining filesystem layers in any order you want. However it doesn't provide compatibility with existing package managers: that's something that you, or someone else in the Dagger community, would implement. You can extend the Dagger API with your own types and functions, then share them as reusable modules.
For example, here's a Dagger module for building Alpine Linux containers in an order-independent way. Under the hood it's derived from the 'apko' build tool created by the folks at Chainguard. https://daggerverse.dev/mod/github.com/dagger/dagger/modules...
And here's a Dagger Shell command for building a container using that module:
github.com/dagger/dagger/modules/alpine | container --packages=git,openssh,curl | terminal
Neat! Okay, yes, I can definitely see the value here, particularly if all or most of an image is otherwise able to be expressed in terms of things that are deterministic, such as language ecosystem package managers with lockfiles.
It seems like you're cutting an interesting track on providing a better way than Dockerfiles with their imperative layers, but pragmatic enough to not insist on taking over the whole world like Bazel or Nix.