title: Run a Flask app forever, even after reboot
body: <p>I have a running Flask app that is working fine on a Linux (CentOS) server.
  To make it work in the background I started it within a <code>screen</code> session. There is scheduled downtime for the server every night. The next day all screen sessions are gone. How can I keep my Flask app or screen sessions always up and running after reboots?</p>