[kevincox]

NixOS is leauges above Ansible and similar. They are barely even playing the same game.

The TL;DR is that Ansible is given a description for some part of the system, then squints at that part and trys to make it match the description. This means that it doesn't unify anything that you haven't described and if you stop describing something it doesn't go away (unless you explicitly tell Ansible to remove it). This means that your Ansible configs end up unintentionally depending on the state of the system and the state of your system depends on the Ansible configs you have applied in the past.

NixOS is logically much more like building a fresh VM image every time you apply the configuration. Anything not in the configuration is effectively gone (it is still on the filesystem but the name is a cryptographic hash so no one can use it by accident). This makes the configs way more reproducible. It also means that I can apply a config to any system and end up with a functional replica that has no traces of the previous system. (other than mutable state which Nix doesn't really manage.)

Nix has other advantages such as easy rollbacks (which is just a bit more convenient than checking out an old config and applying it manually) and the ability to have many versions of a library/config/package without conflicts or any special work required if you need that.

I wrote a blog post a while ago that tries to go a bit more into detail over what I just described https://kevincox.ca/2015/12/13/nixos-managed-system/

[doliveira]

It seems to me that if Nix were a little more beginner-friendly, it could fill a lot of the space Docker occupies.