Applying Domain-Driven Design: From Project Initiation to Architectural Boundaries

1. Terminology

IAAS: Infrastructure‑as‑a‑Service; PAAS: Platform‑as‑a‑Service; SAAS: Software‑as‑a‑Service.

2. Architecture Evolution

The evolution is illustrated by three layers:

SAAS : From monolithic applications to MVC/SSM and layered decomposition to decouple business modules.

PAAS : Extract common technologies (mesh, SOA, micro‑services) to build subsystems efficiently.

IAAS : Scale high‑concurrency services with multiple servers, abstracting OS differences via VM, Docker, Kubernetes.

3. Bounded Context

Bounded Context (BC) defines a domain or module. Different BCs may represent the same concept differently, e.g., a product in an order context versus an inventory context.

BCs relate to technology: aggregation across BCs may require synchronous calls (order‑to‑payment) or asynchronous messaging (event‑driven integration).

4. Four‑Layer DDD Boundaries

First boundary : Define vision, core sub‑domains, generic sub‑domains, and supporting sub‑domains.

Second boundary : Bounded Contexts act as process‑level isolation.

Third boundary : Within each BC, split into Interface, Domain, Application, and Infrastructure layers.

Fourth boundary : Use aggregates in the domain layer to maintain model consistency.

5. Clean Layered Architecture

Separate implementation from interfaces so the domain layer remains independent of technical details, enabling easy replacement of infrastructure components.

6. Hexagonal Architecture

Adapters (controllers, UI, CLI) implement inbound ports, while outbound ports handle storage, external services, etc., forming a polygon of ports and adapters.

7. Onion Architecture

Extends the hexagonal model by further separating the inner business logic into Application Services, Domain Services, and Domain Model layers.

8. Summary

Domain‑Driven Design is a popular architectural approach; following its four boundaries enables clear domain separation, facilitates vertical and horizontal scaling, and provides a solid foundation for future extensions.

来源：blog.csdn.net/qq_32828253/article/details/110673205