Interesting recipe for moving from dedicated servers to the cloud with MongoDB:
You could bring up the new instances on EC2 and add them to the set. Once they were synced, set the priorities of the
dedicated servers to 0 (so they won’t become master), make sure one of the EC2 servers becomes master, and then take the old servers offline.
Original title and link for this post: MongoDB: Scale Out Strategy Question (published on the NoSQL blog: myNoSQL)