Add VRRP/Keepalived support for active/standby set up

[Haw Loeung]

Hi,

In cases where we want to have an active and standby/hotspare/backup OpenVPN server, it would be useful to add support for VRRP/Keepalived to allow automatic or more seamless failing over. The current process is pretty manual:

 * stop OpenVPN on active (though probably not needed).

 * remove assigned VIPs on active.

 * bring up assigned VIPs on standby (either `netplan apply` or manual).

 * start up OpenVPN on standby.

[Junien F (axino)]

What's the client view for when a failover happens ?
Is there maybe a difference between shutting down openvpn on the active one first and not doing that ?

[Haw Loeung (hloeung)]

Actually, thinking more about this one, we should still stop OpenVPN. The difference, I think, is that stopping OpenVPN first tells clients to disconnect and reconnect or retry to reconnect immediately whereas with keeping it up and cutting over would mean that clients would only retry to reconnect on timing out which could be 5-10 mins, maybe even more.