Moving from a VPS host to EC2 with as little downtime as possible

We have a rather large server stack (more than 30 machines), and we can't go on using our curre开发者_运维问答nt VPS provider. we must move, and Amazon's EC2 seems to be our solution.

We use rails, mysql, mongo, redis and other stuff, and we need to move these with as little downtime and with no data loss.

Has anyone here done such a task? anyone with tips on how to do that?

First, MySQL and MongoDB is suppout for write/read replication, write at the current environment and read slave at the new box. Secondly, code in rails is not changed, you may run apps at new node and use DB at the old one firstly and switch DB to new box smoothly.