Architectural coupling

Make sure your architecture matches the problem domain. Don't try to force fit an unsuitable architecture.

Monoliths

Monolithic architectures, particularly layered architectures, are a common choice when starting a project because developers understand the structure easily. However, many monoliths reach end of life and must be replaced because of decreasing performance, size of code base, and a host of other factors. A current common target for monolith migration is microservices-style architectures, which are more complex than monolithic architectures in areas like service and data granularity, operationalization, coordination, transactions, and so on. If a development team has a hard time building one of the simplest architectures, how will moving to a more complex architecture solve their problems?

If you can't build a monolith, what makes you think microservices are the answer?

Simon Brown

Before embarking on an expensive architecture restructuring exercise, architects may benefit from improved modularization of what's already present. If nothing else, it's an excellent starting point for the more serious restructuring that follows.

Microservices

In microservices architecture, the domain encapsulates technical and other architectures, making evolution across domain dimensions easy. No one perspective on architecture is "correct", but rather a reflection on the goals developers build into their projects. If the focus is entirely on technical architecture, then making changes across that dimension is easier. However, if the domain perspective is ignored, then evolving across that dimension is no better than the Big Ball of Mud.

One of the major factors that impacts the ability to evolve an application at the architectural level is how unintentionally coupled each part of the system is. For example, in a layered architecture, architects specifically couple layers together in an intentional way. However, the domain dimension is unintentionally coupled, making evolution in that dimension difficult, because the architecture is designed around technical architecture layers, not the domain. Thus, one of the important aspects of an evolvable architecture is appropriate coupling across dimensions.

Neal Ford, Rebecca Parsons & Patrick Kua, "Architectural Coupling", in Building Evolutionary Architectures: Support Constant Change, 57-58, 74, 78.