Oracle Cloud offers nice free virtual machines, but there was no installation image for NixOS. Luckily NixOS-infect worked really great.
It worked both with Oracle Linux and Ubuntu installations. I prefer infecting Oracle Linux since it leaves a larger /boot partition for kernel images.
Unfortunately the Oracle Linux image also has a large swap partition. If anyone has ideas for how to remove the swap partition and move the XFS root partition so that it can be grown, let me know.