After installing OpenVPN on CENTOS7 you need to create a conf file in [ /etc/openvpn ]

After creating this configuration file you need to enable this VPN configuration for automatically stop and start this service.

So how does is work ?

Say you created the openvpn conf file with the name [ /etc/openvpn/myvpn.conf ]

First enable this vpn service for this specific configuration :

# systemctl enable openvpn@myvpn.service

Then you can start the VPN connection for this configuration :

# systemctl start openvpn@myvpn.service