Legacy Modernization and Architecture Evolution Questions

Evolving an existing system rather than designing greenfield. Covers the modernization patterns (strangler fig, anti-corruption layers, facades and protocol adapters), choosing between rehosting, replatforming, incremental refactoring and a full rewrite, data migration and coexistence (dual-running, change-data-capture versus bulk cutover, reconciliation and drift), cutover readiness and decommissioning, recovering undocumented behavior from legacy code and stored procedures, instrumenting a migration so you can tell in real time whether it is working, and the organizational and risk management of long migrations across many teams. The scope is the migration itself: not quantifying or prioritizing technical debt, not code-level refactoring craft, not how to decompose a system into microservices, and not cloud migration or deployment and rollback mechanics as topics in their own right.