The userdata file is a plain-text file in raw cloud-init format, without compression or base64 encoding.
The maximum file size is 512KB.
Userdata configuration can be used to accomplish a number of configuration tasks in the guest operating system. For instance, some of the more common tasks include:
Add user accounts
Install software
Run scripts
Import SSH keys

#cloud-config

users:
  - default
  - name: testuser
    primary_group: testgroup
    sudo: ALL=[ALL] NOPASSWD:ALL
    groups: sudo, wheel
    ssh_import_id: None
    lock_passwd: true
    ssh_authorized_keys:
    - ssh-rsa myRsaPubKey