The only way ansible could be somewhat like nix is if you reinstalled the same exact version of the target OS each time before you run your playbook. The proble

The only way ansible could be somewhat like nix is if you reinstalled the same exact version of the target OS each time before you run your playbook. The problem is that ansible, puppet, salt, chef, et al, are simply tools to mutate the giant bag of state that is a Linux OS. Even then getting to the same end state is a suspect proposition unless you're extremely diligent in pinning things like exact package versions and ensure tasks run in the exact same order every time. While these tools are good at making certain changes, and are even pretty good at detecting and eliding already-done work, they are _not_ idempotent. There are nearly no modules that properly handle unmaking their changes, so once you mutate that bag of state you're left with a state vector that is barely better than completely undefined. If you're familiar with these tools you have no doubt deployed undo-this-change tasks that you leave in the tasklist until you're fairly confident it's run on every system the do-this-change tasks ran on. Even if a module does attempt to offer an undo-the-state functionality, you can't just remove it, you have to first configure it to run in the "undo" configuration before you remove it.