Nix has a tool called nix-ops that will provision vms on virtual box (you can use containers powered by libvirt as well if you want). It's cool because you can

Nix has a tool called nix-ops that will provision vms on virtual box (you can use containers powered by libvirt as well if you want). It's cool because you can use functional programming concepts and it takes a lot of the support headache away. The option to provision vms is really nice in some cases, which Docker just doesn't give you. But you can also use containers, just like docker, with reproducible builds, which means you can effectively test deployments without ever spending a dime on real hardware.