Asterisk HA

I’ll try and keep this simple.

Multiple Asterisk boxes. Multiple users. UserA is registered with Asterisk box 1 and UserB is registered with Asterisk box 2.

What methods can I employ that would allow each Asterisk box to find the other user? Surely anyone who has looked into Asterisk HA/redundancy has come across this problem. I’d like to get a pointer to some solutions.

I thought maybe we might be able to use Asterisk real time assuming it keeps all peer info common, but from the Wiki:

That rules that out. Gotta have voicemail indications.