I see Docker's DSL as a rather thin layer of abstraction as compared with Nix. Re: declarative vs. functional I believe this does not matter all this much in containerland. As long as I can get sh*t done deterministically, I could not care less about the programming paradigm that got me there.
Docker is non-deterministic. If you and I build the same image, we are not going to get the same result. See https://reproducible-builds.org for more information on the subject.
