Virtual servers break after roboot because local IP address changes

I have installed virtualmin from the script on a clear Amazon AMI image.

Everything installed and works perfectly. I have set up several virtual webservers which work well.

The problem arises when I reboot the server and the local IP address changes.

Amazon allows us to have a static external address, but I have found that when I use this address all requests to any url go to the default virtual server.

How can the virtual servers automatically pick up the new local address ?