Make as much of the app static as possible. Run as much of the logic in the browser as possible. Once you've isolated the "must be on the server" stuff, put an

Make as much of the app static as possible. Run as much of the logic in the browser as possible. Once you've isolated the "must be on the server" stuff, put an intelligent rate limit on it, add auto-scaling with upper limits, and prepare a page to be shown when the server goes down.