I think
Sergey’s answer is good for you.
I was just curious if Sergey knew if his solution supports active call failover as well, which I doubt, but I am not sure.
Failover must be supported on on server side and on client side.
I tested Verto client and may say failover is works on client side.
Also i tested nginx in many cases, failover is works too.
I not tested Verto failover on FreeSwitch side.