Applying Layered Architecture and DDD to Microservice System Design

This article proposes a practical solution that integrates layered architecture and Domain‑Driven Design (DDD) for building complex microservice systems, based on the author’s personal experience.

The recommended five‑layer web service architecture consists of:

Infrastructure layer – provides generic technical capabilities such as persistence, middleware, and third‑party services.

Domain service layer – encapsulates business concepts, state, and rules; each domain module corresponds to a highly cohesive microservice.

Application service layer – defines tasks, coordinates domain objects, and acts as a business data gateway, handling permission checks and data transformation.

Gateway layer – offers external HTTP or protocol services, handling security, monitoring, and request routing.

User interface (presentation) layer – presents data to users or other systems.

The article explains why the gateway layer is essential for separating network concerns from business logic and how it fits into modern front‑end/back‑end separation.

Key design principles include:

Each layer should be cohesive and depend only on the layer directly below it.

Communication from lower to upper layers must go through indirect mechanisms such as middleware.

Upper and lower layers should be loosely coupled, following the Dependency Inversion Principle.

Domain splitting guidelines are provided, emphasizing clear functional boundaries, incremental refinement, and the possibility of virtual domains that aggregate multiple microservices.

A concrete code example demonstrates how an application layer aggregates data from several domain services to build a home‑page response:

Response getHomeData(Request request){
    String nickName = userService.getNickName(request.getUserId());
    OrderInfo orderInfo = orderService.queryLatestOrder(request.getUserId());
    CostTrend costTrend = payService.queryCostTrend(request.getUserId());
    Integer points = pointService.queryAvailablePoints(request.getUserId());
    return new Response(nickName, orderInfo, costTrend, points);
}

The article also outlines a typical development workflow for a SaaS project, from requirement review and prototype preparation to domain design, parallel front‑end and back‑end development, integration testing, and release.

In conclusion, the author stresses that a well‑designed layered microservice architecture, combined with DDD principles, is crucial for large‑scale e‑commerce platforms and invites readers to share their own experiences.