Rewrites frequently fail or go massively over budget/schedule. It can be difficult to fully replicate the existing system and there are frequently important bu

Rewrites frequently fail or go massively over budget/schedule. It can be difficult to fully replicate the existing system and there are frequently important but subtle reasons why the existing system has the architecture it does. To the extent that one can make modular changes and address the most-important pain-points, one probably should. Sometimes a complete rewrite is a better choice, but if embarking on that path, a fail-fast attempt at an MVP might be the right style to do so. If the MVP crushes the existing system in performance/benefits, then subsequent iterative development may yield a viable re-written replacement system.