Instructions based on: https://www.digitalocean.com/community/tutorials/how-to-configure-a-linux-service-to-start-automatically-after-a-crash-or-reboot-part-2-reference
sudo nano /etc/systemd/system/multi-user.target.wants/openvpnas.service
set in "Service"-section
Restart=on-failure
To test setup find main PID
sudo systemctl status openvpnas.service
Kill main process
sudo kill -9 [add PID number here]
Check if process comes back alive
sudo systemctl status openvpnas.service