Vagrant Box
The vagrant cloud has a NixOS box, but it is an older revision and hasn't been updated for a short while[1], it is currently stuck to the much older 16.09 release.
The tooling used to build the boxes is still available and still maintained. It is @zimbatm's nixbox project.
Building a recent box
There are some small caveats with the tooling, one will need to do a bit of work to get it working, and then working in a reliable manner on slower hardware.
First, in the nixos-x86_64.json
file, remove the post-processor of type atlas, unless you want to push the image on the vagrant cloud (you're on your own there).
Then, it may be necessary to increase the boot_wait
a bit, on a Haswell laptop-class CPU, with SSD, 30 seconds was a few seconds too short, doubling is almost sure to be enough for most uses. This is only used once during the build of the .box file.
Then, continue with the instructions in the README.
NixOS Plugin
The vagrant-nixos-plugin project adds nix provisioning for NixOS guests in vagrant. The project's README should explain its use.