Kolla TLS

Reading the Kolla docs it says: The back-end TLS cert/key can be the same certificate that is used for the VIP, as long as those certificates are configured to allow requests from both the VIP and internal networks. But there is no advice on how to do this, can someone explain how to use letsencrypt vip certs for backend tls, i have found nowhere that explains it at all. Trying to use a self signed cert for backend tls seems to break everything when using proper certs for vips