Strangler Fig Pattern

A way of replacing a legacy system without a rewrite: put a facade in front of it, route one capability at a time to a new implementation behind the same facade, and retire the old system when nothing routes to it any more

Martin Fowler's name, from the fig that grows around a host tree until the host is gone and the fig stands on its own. The alternative — the big-bang rewrite — fails often enough to have its own literature. The pattern's cost is the facade and the months of two systems running; its return is that every step ships, every step can be measured, and stopping halfway leaves a working system. A design-system migration is a strangler fig by nature: one component at a time behind the same contract, the old library retired page by page.