You could use NixOps[0] for Nix but I'm not sure you can directly compare Terraform and Guix/Nix? My set up involves Terraform for infrastructure and Nix for provisioning, and it's working for me so far.

[0] https://github.com/NixOS/nixops

I think this too, but at the same time the reality is a tool like Terraform is really complicated to implement well, and, importantly, it always has to work. All the time. There are really high standards for this, and in my personal experience, alternative solutions like NixOps don't quite stack up in reliability or broad utility versus Terraform. The design is good in theory, but it needs just a huge amount of work to be trusted.

For the most part, I provision things with Terraform and then instantiate the servers with NixOS/Nix itself, and this mostly works. For bonus points you can use Nix to generate the HCL that Terraform reads in (because Nix can write JSON, and HCL is just JSON in a trenchcoat) if you want to put some veneer on it.

You can deploy and manage NixOS on Big Cloud using Terraform: https://nix.dev/tutorials/deploying-nixos-using-terraform.ht...

Are there any providers that to have such integration? I have only lightly used nix. Having a hard time understanding what a cloud provider integration would look like.