Microservices Decomposition Strangler Fig Pattern and API Gateways

Lecture 35 of SE602 Software Re-Engineering investigates contemporary microservice decomposition techniques that systematically replace legacy monoliths without incurring catastrophic system outages. The lecture focuses on Martin Fowler celebrated Strangler Fig pattern, where new business capabilities are developed as independent microservices while an API Gateway intercepts external traffic, routing requests either to the legacy system or to newly deployed microservices. Over time, features are progressively strangled from the monolith until the legacy core can be safely decommissioned. Students study distributed data management challenges, moving from shared monolithic databases to database-per-service architectures using event-driven synchronization and the Saga pattern for distributed transaction management. Database schema normalization, legacy record migration, and automated ETL extraction pipelines are systematically analyzed. Monolithic application decomposition strategies including service-oriented architecture (SOA) and the Strangler Fig pattern are examined in depth. Scholars examine program slicing algorithms, forward and backward dependency slices, and impact assessment for proposed modifications. Automated tool support, bytecode instrumentation, and static code analyzers are evaluated to detect architectural violations across repositories. Risk management frameworks, business case evaluations, and cost estimation models such as COCOMO II are analyzed for migration projects. Legal and ethical constraints surrounding reverse engineering, clean-room design implementations, and software intellectual property rights are reviewed. By engaging with solved past papers by Moaaz and Waqar Siddhu, learners gain actionable insights into recurrent university exam questions. Interactive quiz assessments on VU SIGMA facilitate rapid knowledge verification and retention of critical software re-engineering concepts. Comprehensive coverage of standard academic benchmarks ensures learners communicate with technical precision across software engineering disciplines. Detailed analysis of code smell topologies highlights the imperative of eradicating duplicate logic, long methods, and bloated god classes. Test harness construction including characterization testing and regression suites are contrasted with traditional unit testing strategies. Students evaluate the trade-offs between big-bang system rewrites and progressive evolutionary refactoring in mission-critical environments. The lesson explores cognitive program comprehension models, top-down hypothesis validation, and mental mappings of complex legacy architectures.