A good re-engineering of any legacy system starts with logging. Reading code is simple, just use your eyes. But understanding what the code actually does requir

A good re-engineering of any legacy system starts with logging. Reading code is simple, just use your eyes. But understanding what the code actually does requires knowledge of not just code but also data. The data that actually flows through the system on a regular basis and how it gets transformed from one function call to the next. The next necessary step is piecemeal migration. You're not going to be able to process all request types from the get go. Start with building a new system that handles form A and leave forms B through Z to the existing system. The next project will be to tackle form B, and so on. If either of these steps isn't possible (due to dysfunctional management, usually) then the project is doomed to fail.