I have a webapp running in a Media Temple VPS account, and I'm currently evaluating the gains to switch to Amazon EC2. It's running under Apache 2 web server.
This webapp for now has almost no access normally, with some big utilization peaks, which are known with some days of notice.
Right now at Media Temple we have a server with 2GB of Memory, which is enough for those big utilization peaks. As we move to Amazon, I'm thinking maybe of having two instances - a micro for normal use, and a Small or even Medium for the peaks.
I'm trying to figure out the best way to do this in a way this could work. At first, I could maybe change the DNS, routing the clients to the bigger server when those peaks come. But this would be quite dangerous in my opinion, so I'd like to know how this can be done correctly.