Halo is a full-stack content management system (CMS) and blogging platform built on Spring Boot WebFlux (reactive) and Vue 3. It provides a Kubernetes-inspired extension model for defining custom resources (posts, pages, comments, attachments, themes, plugins) with automatic RESTful CRUD endpoints, indexing, and reconciliation controllers. The system features a plugin architecture (PF4J-based) that allows third-party extensions to contribute UI bundles, security filters, notification handlers, search engines, and theme template processors. The frontend is split into an admin console and a user center, both built with Vue 3, FormKit, TanStack Query, and a rich-text editor (Tiptap). Security includes multiple authentication methods (password, OAuth2, email code, TOTP two-factor), RBAC authorization, remember-me, device management, and sudo confirmation. The theme engine uses Thymeleaf with custom dialects and a finder pattern to expose backend data to templates. The codebase is large but well-organized, with clear separation between API interfaces and implementations, extensive use of reactive programming, and a strong emphasis on extensibility through extension points.