Create more users than the image default on instance creation
#cloud-config users: - default - name: username gecos: Full Name Here groups: sudo sudo: ALL=(ALL) NOPASSWD:ALL ssh_authorized_keys: - ssh-ed25519 <key> <comment> - ssh-rsa <key> <comment> - ...
If you don't include the "default" entry first in the users-block, the default user for the given image will NOT be created. Therefore: keep it. Full documentation on this, here
Add additional SSH keys to the default user
#cloud-config ssh_authorized_keys: - ssh-rsa <key> <comment> - ssh-ed25519 <key> <comment>