> I just wanted to like "terraform apply" a system configuration on my Debian install.
I think 'like Terraform, but for the system configuration' is an apt description of NixOS. -- i.e. NixOS is a Linux distribution built around using Nix to generate the system config.
The Nix package manager itself happily works on other Linux distributions. (And on macOS).
> ... Ansible ...
Nix's main focus is on packages. It happens to incidentally do package-related stuff quite well, which is why nix also gets used to declare development environments, build Docker/VM images, or used to configure NixOS.
An interesting set of terms related to Ansible vs NixOS: Ansible is 'congruent', in that it tries to get a system to a desired state by comparing what's there with what it expects. Whereas, NixOS is 'congruent', in that the system is built to be in the desired state.
> But not the "Nix system config manager", which is grouped under the same set of CLI tools, is that right?
The `nixos-rebuild` command is what you'd use to apply a NixOS configuration (that's NixOS only). (I believe it's possible to run the command to build a configuration on non-NixOS).
Whereas, the other nix CLI programs are mainly `nix-build`, `nix-shell`, etc. which are now grouped under a single `nix` command.
> Packages or system configuration or both?
I'd say packages.
That people like NixOS for its declarative system configuration is incidental.
Nix's key idea is symlinking everything. You put a package in some directory under /nix/store, where the address is computed from that package's inputs. (e.g. what compiler to use, what compiler flags to use).
If you build the same package with different inputs (e.g. different compiler versions), these packages can exist alongside each other in /nix/store. Nix can then build a PATH using whichever package you want to use. It's able to come up with ~/.nix-profile/bin and ~/.nix-profile/include (and share, etc.), symlinking to the stuff in /nix/store.
NixOS essentially 'just' applies that idea, but symlinks stuff under /etc to whatever /nix/store package has the system configuration. (Plus uses systemd services, and a few other things).
e.g. when I `readlink /etc/hosts`, it resolves to `/nix/store/n5ijm9zzkcm7qglsqrfvnixih0q7dskb-host`, or /etc/fstab to /nix/store/xb7jmzd0wy0wy4vihh0q17m81kmqgc7y-etc-fstab.
I think 'like Terraform, but for the system configuration' is an apt description of NixOS. -- i.e. NixOS is a Linux distribution built around using Nix to generate the system config.
The Nix package manager itself happily works on other Linux distributions. (And on macOS).
> ... Ansible ...
Nix's main focus is on packages. It happens to incidentally do package-related stuff quite well, which is why nix also gets used to declare development environments, build Docker/VM images, or used to configure NixOS.
An interesting set of terms related to Ansible vs NixOS: Ansible is 'congruent', in that it tries to get a system to a desired state by comparing what's there with what it expects. Whereas, NixOS is 'congruent', in that the system is built to be in the desired state.
https://flyingcircus.io/blog/thoughts-on-systems-management-...