This is your personal opinion, a rolling release like NicOS is exactly the opposite of an LTS distro.

I actually wonder what would happen to a NixOS installation frozen in time for 5 years that then you want to update to latest all of a sudden.

I've only been running NixOS (in any serious capacity) for three years, but I have installed it on every computer that I am allowed to install it on now.

It has been the most headache-free Linux I've used, simply because I'm less scared to play with and fix stuff. The fact that rollbacks are trivial and snapshots are automatic, and since everything is declarative in a text file anyway, I am way braver. If I do something like screw up the video driver, or the wifi driver or make it so the system doesn't boot anymore, all I need to do is reboot and choose a previous generation.

Earlier today, I tried to run a simple nix tool a colleague made. 3 hours into the build, it crashed. Something about a missing python import? I ran the exact same ‘nix develop’ again. 2 hours later, it worked.

Keep in mind: this was just a simple rest server. But for some reason it needed to (nondeterministically) build the word from scratch to send that single request.

I’ll take a docker system thank you.

I have run NixOS for about eight years on server and desktop and been a nixpkgs maintainer. Yes, most of the time I would agree with you. The fact that you get warnings in the terminal for a lot of incompatibilities and changes when upgrading is a really nice touch and upgrades tend to be smooth. I do not use rollbacks much, but when you do need them they are really handy. Having every configuration in a single file makes you more bold to play around with configurations, which felt really empowering when I first got into NixOS, as I knew it could roll things back and I no longer had to keep notes on how each box was set up to refer to in the case of a reinstall or migration.

However, I have had one machine become unbootable as it could no longer mount its encrypted disks after an upgrade, forcing me to mount a rescue image remotely, mount the disks manually, lift the data out, and do a complete reinstall (migrated the box to OpenBSD at that time). Similarly, NixOS once messed up systemd (or vice versa) so badly that I could not even reboot without forcing a power cycle. Lastly, I have had a package break for my use cases by maintainers enabling so many custom flags by default for a package that they enabled one I have never seen enabled by any other packaging team and that then broke RTSP in "funny" ways. Ubuntu did tend to break things like graphics between releases at times back when I used it, but I have never had any other distribution or operating system throw curve balls like the three things I mentioned here.

My general impression of NixOS is that the core is solid, but that nixpkgs just has such a large number of things that it supports that the maintainers struggle to test them all and can not anticipate the interactions between all the packages and options. The default Julia package being so broken that it produced incorrect mathematics due to nixpkgs' insistence on allowing you to swap out the Blas library and also having turned off the unit tests for example springs to mind. This was shipped to end users for a long time before I noticed it by accident by enabling the unit tests and stepped in to clean it up. It all feels very "Gentoo", which was indeed an inspiration for NixOS by the way.

Now, return to that last sentence in the first paragraph that I wrote about feeling empowered to tinker, ultimately, I feel like you should try to resist that urge as it is what pushes you into the untested fractal of possible configurations that NixOS allows you to explore. My other main operating system is OpenBSD, where the mentality is "Stick to the defaults or suffer the consequences"; with NixOS, I feel like everyone's box is more or less a tailored suit, which comes with both its ups and downs.

I run nixOS as well on my home infrastructure (gateway/firewall, a couple of internal servers).

But I have had, uh, non-trivial breakages happen also when I upgrade the system itself to the next yearly release. Non-bootable kernel kind of breakages.

But I will give you that I can just boot from the generation before the upgrade, and it works again. So there's that :)

Eh nix flakes are a nightmare to configure. Far more verbose than a docker compose. They rely on some caches which keep pre-compiled packages and you better make sure you have the caches with the particular flakes you need set up. Yikes