I created a web application using NGINX, Rails, and MySQL. Currently they are all running on a single VPS (Slicehost). I've followed best practices and maintained a very minimal 'shared-nothing-architecture' with the idea that if I need to scale, I'll simply ramp up a few more slices to meet demand.
With the idea that I am trying to keep costs as low as possible, what would be a good strategy for bringing on additional slices on an as needed basis? My initial thoughts are that I should run 3 VPSs. Two for databases in a master/slave configuration, and one for NGINX/Rails. As load increases, ramp up other NGINX/Rails servers as required with the original server handling the load balancing to the other servers.