Decomposing Monolithic Applications into Microservices: Business Capability, Subdomain, and Strangler Patterns

When designing large concurrent applications or refactoring legacy systems, the first consideration is often a microservice architecture.

Microservices split an application into a series of loosely coupled services, enabling continuous delivery and flexible deployment to accelerate software development.

Decomposition is important because it promotes division of labor and knowledge sharing, and it clarifies how multiple elements interact.

There are two project types: Brownfield projects (re‑development of existing or legacy systems, such as converting a monolith to microservices) and Greenfield projects (building a brand‑new system without legacy constraints).

Decomposition by business capability involves breaking the system according to stable business functions—for example, order management, inventory, payment, and shipping in an e‑commerce platform. This approach yields stable business logic, cross‑functional autonomous teams focused on delivering business value, and loosely coupled, cohesive services.

Decomposition by sub‑domain (DDD) classifies domains into Core, Supporting, and Generic sub‑domains, each with relatively stable responsibilities. The benefits mirror those of the capability approach: stable architecture, cross‑functional autonomous teams, and loosely coupled services.

When splitting a monolith, common challenges include network latency between services, maintaining data consistency across separate databases, and the emergence of a “God class” that centralizes too much logic.

The Strangler pattern offers a gradual migration strategy: new services replace specific functionalities of the monolith, and once a new service is ready, the old component is retired, allowing a smooth transition to a fully microservice‑based system.