Very simple way: set up a small Linux instance and install Nagios on it. Configure a FTP probe in Nagios, and configure a notification to a user on the VM system. The Nagios system will test the FTP server by connecting and attempting to transfer a small file periodically. If it fails, it sends a notification email. Handle the email with PROP.
That approach tests not only whether the server is logged in, but whether it's actually functioning. Works well for lots of things, and is low-cost (no cost if you run Debian or Fedora for Z).
