Strangler Fig Pattern

The Strangler Fig Pattern is a migration approach that replaces an existing system gradually instead of rewriting it in one large project. The metaphor comes from a fig that grows around an older tree and eventually takes its place. In software architecture, new functions, interfaces, or workflows are built alongside the legacy system. A router, API layer, or event stream then sends more traffic to the new components while the old parts are retired in controlled steps. The pattern is especially useful for AI-assisted modernization. Agents can inspect individual modules, add tests, stabilize interfaces, and prepare migration steps without forcing the whole system to change at once. That lowers delivery risk because every stage can be reviewed, tested, and rolled back. The hard part is not writing new code; it is choosing clean boundaries, maintaining observability, preserving fallback paths, and sequencing the work realistically. The pattern does not fit every project, but it is often safer than a big-bang rewrite that consumes months before proving whether the new system works.