Page Carnival is a Spring Boot book marketplace architecture featuring role-based access control for admins, sellers, and buyers through Spring Security and custom authentication handlers. Client requests flow through a Security Filter Chain into MVC controllers serving Thymeleaf templates and REST API controllers returning JSON, with cross-cutting concerns like @PreAuthorize and @Valid enforced at the controller layer. The Service Layer (AuthService, BookService, CartService, OrderService) orchestrates business logic and delegates data access to Spring Data JPA repositories connected to PostgreSQL 15. The entire application is containerized with Docker and deployed via GitHub Actions CI/CD to Render Cloud, demonstrating a production-ready layered architecture with separation of concerns. Fork this diagram to customize role hierarchies, add new services, or adapt the deployment pipeline for your own marketplace platform.