StranglerPattern

Strangler Pattern, also called the Strangler Fig Pattern, is a software migration approach in which a legacy system is gradually replaced by new functionality. Instead of rewriting the entire application in a single big bang effort, new components are built alongside the old system and progressively strangle it by taking over more routes and features until the original system can be retired.

Implementation typically starts by identifying a migration path—one module, feature, or user journey at a time. A routing layer, facade, or API gateway forwards calls to either the legacy components or the new services. As each piece of functionality is implemented in the new system, the corresponding path in the old system is decommissioned. Over time, the old monolith is replaced piece by piece, and the overall architecture shifts toward the new design, such as microservices or modular services.

Benefits include reduced risk compared with a complete rewrite, ability to deliver value early, and the option to adopt newer technologies incrementally. It also helps maintain availability during migration and provides a clear rollback point for each feature. Drawbacks include increased architectural and operational complexity, data synchronization challenges between old and new systems, potential performance overhead from routing, and the need for strong governance, testing, and monitoring during the transition.

Common use cases include migrating large monolithic applications to service-oriented or microservice architectures, web portals, or any system where gradual replacement of functionality is preferable to a single redevelopment effort.