Strangler Fig Migration (TypeScript, NestJS, Express, PostgreSQL, Redis, Docker) overview

A migration architecture implementing the Strangler Fig pattern to incrementally replace a legacy monolith with modern TypeScript services. An Express reverse proxy intercepts all traffic, routing requests to either the legacy system or new NestJS microservices based on feature flags and path matching. Redis caches routing decisions and shared session state between old and new systems. PostgreSQL serves both the legacy schema and new service schemas, with CDC (change data capture) keeping them synchronized during the transition. Docker Compose orchestrates the complete hybrid environment locally. The tradeoff is maintaining two systems simultaneously with careful data consistency management, but the pattern eliminates big-bang migration risk.