Sync posts to a backup blog for failover

I have a friend that has a wordpress blog on a host that constantly goes down due to them being sold to another company, and I’d like to host a backup of his blog on my host as a failover when his datacenter goes out.

What I’m looking for is a way to automatically sync the posts over when they are made, and have the dns fall over (which is easy enough) to the second server when the first goes down. I’ve done quite a bit of searching, but haven’t found a way to make this possible.

Has anyone done this, or have suggestions for doing so? I’d appreciate it. Thank you.