[zbentley]

> Docker ships a "filesystem in a box", i.e. an opaque blob, an image. Nix and Guix ship the package definitions from which they derive what they need to have populated in their respective stores, and either build those required packages or download pre-built ones from somewhere else, depending on configuration and availability.

The rest of your endorsement of NixOS is well taken, but this is a silly distinction to draw. Dockerfiles and nix package definitions are extremely similar. The fact that docker images are distributed with a heavier emphasis on opaque binary build step caching, and nix expressions have a heavier emphasis on code-level determinism/purity is accidental. The output of both is some form of a copy of a Linux user space “in a box” (via squashfs and namespaces for Docker, and via path hacks and symlinks for Nix). Zoom out even a little and they look extremely alike.