pattern: a way to incrementally modernize a legacy system as defined by Martin Fowler.  Instead of building an entirely new system, we take a small piece of the legacy system and rebuild it in a way that lets the rest of the legacy system. We launch that piece into production and have users use it seamlessly as if it is part of the legacy system.  Then we take another piece out of the legacy system and do do the same thing. And another. And another. Until eventually there is nothing left of the legacy system—it has vanished, piece by piece, like Alice in Wonderland’s Cheshire Cat.  The strangler pattern