Spec-Driven Application Modernization: Transform Monoliths, APIs, Databases, Runtimes, and Infrastructure with Executable Specifications, AI Coding Agents, ... (Spec-Driven AI Engineering Series)

Spec-Driven Application Modernization Modernize critical software without betting the business on a rewrite. Legacy applications rarely fail because every line of code is old. They become difficult because business rules, data dependencies, APIs, deployment assumptions, and operational knowledge accumulate faster than teams can safely change them. Spec-Driven Application Modernization gives you a practical, production-focused approach for transforming those systems incrementally—with executable specifications, AI coding agents, controlled migration, and evidence-driven verification guiding every major decision. Through the connected Ridgeway Commerce Platform project, you will modernize a production-shaped monolith from end to end. You will learn how to: Assess legacy applications and choose what to refactor, replatform, extract, replace, retain, or retire. Establish behavioral baselines and executable modernization specifications before changing critical code. Create modular boundaries, compatibility façades, and strangler-pattern routing for safe coexistence. Govern AI coding agents with explicit scope, invariants, tests, and evidence gates. Upgrade Java, Spring, frameworks, dependencies, and application architecture without uncontrolled rewrites. Decide when microservices create real value—and when a modular monolith is the better design. Modernize APIs, asynchronous workflows, integrations, and shared databases using expand-and-contract migrations, transactional outbox patterns, reconciliation, and explicit data ownership. Build portable containerized runtimes and specification-gated CI/CD pipelines. Prove production readiness with security checks, observability, reliability evidence, shadow traffic, canary releases, rollback triggers, and controlled cutovers. Retire legacy infrastructure only after evidence proves it is safe. At the center of the book is the MODERN Method: Map, Outline, Decouple, Evolve, Release, and Normalize—a repeatable framework for turning modernization into a sequence of bounded, verifiable decisions. All essential code, commands, configurations, specifications, templates, architecture references, and troubleshooting guidance are included in the book, so you can follow the complete modernization journey without relying on an external repository. Whether you are a software developer, architect, technical lead, platform engineer, DevOps engineer, SRE, consultant, or engineering manager, this book will help you transform legacy software while preserving the business behavior that made it valuable in the first place. Modernize deliberately. Migrate incrementally. Verify with evidence.