Install NixOS on Amazon EC2
Amazon EC2 is a widely used cloud deployment platform that is part of Amazon Web Services (AWS). NixOS largely supports the platform through AMIs and the nixos-generators project.
Public NixOS AMIs
A list of NixOS AMI's available on AWS is located here and for a more up to date list: here (cf. this discourse thread).
The default user for these AMI's is root. There isn't a default password, instead authentication is done by using the SSH key selected during the EC2 creation process.
Creating a NixOS AMI
The nixos-generators project is currently the best method to create your own NixOS AMI. Follow the directions provided by nixos-generators & then follow the instructions provided by AWS.
Additional Resources
Building and Importing NixOS AMIs on EC2 by Jack Kelly
Troubleshooting
SSH Asks For Password
When connecting to a newly launched EC2 instance via SSH, it may ask for a password. This seems to be because the amazon-init systemd service is still reading user data. Back out of the current SSH attempt and try again in a few minutes.