Building resilient large-scale applications

The principles for writing software are the same, but the development process itself is quite different when doing it for small versus large applications. Reading, fixing, and building on a small codebase is easier and more forgiving than in large ones. I have worked on applications from small clients, greenfield applications as well as large-scale ones, serving thousands of users. The difference is that, when there is already a fully operational machine running, mistakes are more costly and dow