About fault isolative architectural structures

There are four general principles for designing and implementing swim lanes in a system’s architecture:

1. There must not be any shared hardware or software between lanes other than possibly highly available network gear such as paired load balancers or border routers. (Nothing is shared)
2. No synchronous calls can take place between swim lanes. If cross swim lane communication is required, i.e. grabbing search results to display on the same page as login, it must be done asynchronously. (Nothing crosses a swim lane boundary, Transactions occur along swim lanes)
3. Limit asynchronous communication. While permitted, more calls lead to a greater chance of failure propagation.
4. Use timeouts with asynchronous calls. There is no need to tie up the user’s browser or your server waiting for the eventual TCP timeout.

A Cheat Sheet-
Swim lane the money maker
Swim lane the problem areas
Swim lane natural barriers

--- From the book Scalability Rules.