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 firstname.lastname@example.org
Then you can start the VPN connection for this configuration :
# systemctl start email@example.com