What are the solutions for clustered VPN?

Question

VPN

Shake everyone.
I am studying the issue of raising a VPN server in a cluster, but there is, as always, a nuance. I really want him to be able to do session migration. For example, there are 3 sites with their own servers, and each has a VPN instance (or maybe not even one). All sites are connected into a single routable network (by means of gre and ipsec). The user connects to the VPN and gets access to all 3 sites (well, or not all 3, it will depend on the user's access there). And now, for some reason, I want to reduce the number of instances of the VPN server, those on one of the sites disable it. And now the question is - is there a complete VPN solution that allows users to migrate between instances without breaking the session in order to decommission one of the instances?
PS I forgot to add that clients can use different operating systems, but Windows, Linux, Mac OS, ios, android will suffice
. PPS And I forgot. Now everything is done on openvpn and everything would be fine, since the system for storing user rights and automatic firewall management, and centralized accounts are fastened. Yes, a lot has been done. But such a killer feature is not enough at all. And there are reasons for that.

Answer 1

And what's wrong with breaking a session if both the client and the server process it correctly and without shouting to the user?

Answer 2

https://pritunl.com/
But only in the paid version for 10 bucks a month.