Glossary
Also: Strangler fig pattern
A pattern for replacing a legacy system step by step: new functionality grows around it, the old system shrinks, until nothing of it is left.
The name comes from the strangler fig, which grows up a tree, encloses it, and eventually stands on its own. Applied to software: a router sits in front of the legacy system and sends individual calls to new code. Few at first, more over time, until nothing runs through the old path.
The alternative is the big rebuild: develop in parallel for two years, then switch. That sounds cleaner and regularly fails, because the old system keeps living and changing in the meantime.
In practice the pattern needs three things: a place where traffic can be redirected, clarity about which data belongs to whom, and the discipline to actually delete the old path after switching.
How you notice it
Frequently asked
Longer than a rebuild on paper and shorter in reality, because parts are in production from the first month. For the publishing platform in my case studies the modernization ran over twelve months without a day of downtime. What matters is not total duration but that every step has value on its own.