Making the systemd service file

See: https://blog.miguelgrinberg.com/post/running-a-flask-application-as-a-service-with-systemd

Useful: https://containersolutions.github.io/runbooks/posts/linux/debug-systemd-service-units/

   sudo nano /etc/systemd/system/myflaskapp.service

[Unit]
Description=<a description of your application>
After=network.target

[Service]
User=<username>
WorkingDirectory=<path to your app>
ExecStart=<app start command>
Restart=always

[Install]
WantedBy=multi-user.target

When the service file is new or changed, you need (one time) to:

   sudo systemctl daemon-reload

Then you can:

   sudo systemctl start myflaskapp
   sudo systemctl status myflaskapp
   sudo systemctl restart myflaskapp
   sudo systemctl stop myflaskapp

Then finally when you see that start works (checking status, checking that it actually is running , etc)

   sudo systemctl enable myflaskapp

Will make the "service" auto start when the pi restarts.

To view the log file (errors):

   sudo journalctl -u myflaskapp -f