Hot Spares with Virtualmin

I've been trying to come up with some way to create a "hot spare" setup where I have a machine that has backups of a server that's running in another data center that can be popped into production should the main machine go down. From what I understand, the only sure fire way is to rsync server backups to the remote server and restore them. Is this true? I just can't think of any other way. Also, how should DNS work for a hot spare setup? Should I have just one nameserver entry (IE just ns1.sample.com) that somehow links to both servers' DNS server, or should I have it setup so that each one has a nameserver entry? (IE ns1.sample.com and ns2.sample.com)

Thanks in advance