4 Thinking in Layers: Separating the 'How' from the 'Why' at Scale
This chapter covers
- What layers are and how they work in architecture.
- Applying the downward dependency rule to create loosely coupled layers.
- Handling cross-cutting concerns like logging and authentication.
- Recognizing common anti-patterns in layered architectures.
- Visualizing layers with a simple diagramming technique and exploring parallels with network layering.
4.1 Introduction
In the first three chapters, we built our foundation. Chapter 1 gave us the Architectural Thinking Process; Chapter 2 filled our toolkit with tools such as ADRs and the “-ilities”; and Chapter 3 armed us with fundamental structural principles such as Separation of Concerns and SOLID. We learned how to make good decisions and how to build well-structured individual components.
Now, it’s time to zoom out. How do we organize all those well-built components into a cohesive, maintainable application? How do we structure the system as a whole?
One of the most powerful and time-tested techniques is thinking in layers. No, not your mother’s lasagna or seven-layer taco dip; we’re talking about architectural layers. This chapter explores how layering helps us apply Separation of Concerns on a grander scale, manage complexity, and build applications that are easier to understand, test, and evolve. We’ll look at the layered approach, the rules that make it work, and how it helps us avoid common pitfalls.