When trying to enable the NFS service, it returns in an error like this:

[root@opennebula01 ~]# systemctl enable nfs
Failed to execute operation: No such file or directory
[root@opennebula01 ~]#

You need to enable something else:

[root@opennebula01 ~]# systemctl enable nfs-server.service
Created symlink from /etc/systemd/system/multi-user.target.wants/nfs-server.service to
/usr/lib/systemd/system/nfs-server.service.

And maybe even start it:

[root@opennebula01 ~]# systemctl start nfs-server.service

Cheers,
TK