This is the same thing I was asking. As much as I like the idea of declarative functional package manager what value does it provide if you are just building docker images?
1. Better abstraction (e.g. the example of a function that produces docker images).
2. The Hydra build/CI server obviates the need for paying for (or administering a self hosted) docker registry, and avoids the imperative push and pull model. Because a docker image is just another Nix package, you get distributed building, caching and signing for free.
3. Because Nix caches intermediate packages builds, building a Docker image via Nix will likely be faster than letting Docker do it.
4. Determinism. With Docker, you're not guaranteed that you'll build the same image across two machines (imagine the state of package repositories changing -- it's trivial to find different versions of packages across two builds of the same Dockerfile). With Nix, you're guaranteed that you have the same determinism that any other Nix package has (e.g. everything builds in a chroot without network access (unless you provide a hash of the result, for e.g. tarball downloads))
1. Better abstraction (e.g. the example of a function that produces docker images).
2. The Hydra build/CI server obviates the need for paying for (or administering a self hosted) docker registry, and avoids the imperative push and pull model. Because a docker image is just another Nix package, you get distributed building, caching and signing for free.
3. Because Nix caches intermediate packages builds, building a Docker image via Nix will likely be faster than letting Docker do it.
4. Determinism. With Docker, you're not guaranteed that you'll build the same image across two machines (imagine the state of package repositories changing -- it's trivial to find different versions of packages across two builds of the same Dockerfile). With Nix, you're guaranteed that you have the same determinism that any other Nix package has (e.g. everything builds in a chroot without network access (unless you provide a hash of the result, for e.g. tarball downloads))