“Clean Architecture” is interesting not because of the circles, but because of the question behind them: what should a system actually depend on? The book is about keeping business logic resilient while databases, frameworks, interfaces, and delivery mechanisms keep changing around it.
Inside a service, it gives a very practical frame for module boundaries, dependency direction, SOLID, cohesion, coupling, and plugin-style thinking. That helps teams separate domain logic from infrastructure details instead of letting the codebase collapse into a tangle of controllers, integrations, and use cases.
In interviews and reviews, the chapter adds depth inside the system. It lets you discuss not only the outer design, but the internal structure as well: where responsibilities sit and why dependencies should point in a particular direction.
Practical value of this chapter
Module boundaries
Teaches clear boundaries between domain, application, and infrastructure to reduce coupling.
Dependency direction
Builds dependency discipline so business logic is insulated from framework details.
Evolvable code
Keeps systems easier to test, refactor, and extend as product scope grows.
Interview depth
Enables strong discussion of internal service design beyond high-level architecture sketches.
Source
Review on tellmeabout.tech
Article from the Code of Architecture club - part 1
Clean Architecture: A Craftsman's Guide to Software Structure and Design
Authors: Robert C. Martin
Publisher: Pearson, 2017
Length: 432 pages
Uncle Bob's classic on structural value, programming paradigms, SOLID, component cohesion and coupling, and plugin-style architecture.
Introduction: Design and Architecture
The opening chapter makes a simple but demanding claim:
"When software is done right, it requires a fraction of the human resources to create and maintain. Changes are simple and rapid. Defects are few and far between."
Architecture = Design?
Martin treats architecture and design as one continuous spectrum of decisions, from large system boundaries down to low-level implementation details.
Main conclusion
“The only way to go fast is to go well” means speed is not the alternative to architecture. It is one of the outcomes of getting the structure right.
Related book
A Philosophy of Software Design
Ousterhout also talks about dealing with complexity and strategic programming
Two aspects of software value
Every software system creates value in two different ways:
Behavior
This is the functional side of the system: what it does for the business and the user. Teams usually experience this as the urgent part.
Structure
This is the structural side: how easy the system is to change, test, and extend. It is important, but often treated as less urgent.
The author frames this conflict through the Eisenhower matrix. In practice, teams often let urgent feature work crowd out architectural decisions that determine the long-term cost of change.
"It is the responsibility of the software development team to assert the importance of architecture over the urgency of features."
Programming Paradigms
The book makes an important point here: each paradigm matters not because of what it enables, but because of what it forbids. Those constraints shape architecture:
| Paradigm | Limitation | Advantage | For architecture |
|---|---|---|---|
Structured Programming | Ban goto | Decomposition into testable functions | Functional decomposition |
Object-Oriented Programming | Safe polymorphism | Plugin-style structure and dependency inversion | Component separation |
Functional Programming | Immutability | Fewer race conditions and hidden side effects | Separation of mutable and immutable state |
Structured Programming
Dijkstra showed that programs can be expressed through three basic control structures:sequence,selection, anditeration. For architecture, that matters as the basis for clear decomposition and testable control flow.
"Testing shows the presence, not the absence, of bugs" — Dijkstra
Object-Oriented Programming
OOP combines encapsulation, inheritance, and polymorphism. From an architectural point of view, polymorphism matters most because it enables dependency inversion and lets details evolve more independently.
"OO is the ability to gain absolute control over every source code dependency in the system."
Functional Programming
Its core idea is immutability. Architecturally, that means fewer race conditions and deadlocks, and it naturally connects to patterns such as Event Sourcing.
"Event sourcing is a strategy wherein we store the transactions, but not the state."
Part 2
Review on tellmeabout.tech
SOLID and component principles
Design Principles (SOLID)
The SOLID principles help build mid-level software structures that are:
- easy to change without a cascade of side effects
- easy to understand
- strong foundations for reusable components
SOLID principles
Click on the letter for details
SSingle Responsibility Principle
Not "a function should do one thing", but a module must be responsible to one actor. Symptoms of the violation: accidental duplication and merge conflicts.
OOpen-Closed Principle
An artifact should remain open to extension while protecting stable behavior from constant rewrites. That is one of the forces that drives architecture in the first place.
LLiskov Substitution Principle
Subtypes must remain interchangeable with the base type. Once that promise breaks, code starts accumulating special branches for every implementation.
IInterface Segregation Principle
Clients should not depend on methods they do not use. At the architecture level, that means avoiding dependencies on oversized components and oversized contracts.
DDependency Inversion Principle
The most flexible systems are the ones whose source code dependencies point only to abstractions. Factories help move concrete construction details out of policy code.
Dependency Inversion with a factory
How abstractions and factories reverse dependency direction
Problem: direct dependence
Application directly depends on ConcreteImpl, so policy is tied to implementation detail.
Related book
Fundamentals of Software Architecture
Richards and Ford continue the discussion of coupling and coordinated change through Connascence
Component Principles
Components are units of deployment. One of the book's strongest takeaways is that long-term architecture tends to move toward stable cores surrounded by replaceable details.
Component Cohesion
Three principles govern how to break down classes into components:
REP
Reuse/Release Equivalence
Classes released together should share a clear theme or reason to live together.
CCP
Common Closure
Group together classes that tend to change for the same reason and at the same time.
CRP
Common Reuse
Do not make component users depend on behavior they do not actually need.
Tension Diagram: Component Cohesion
Architects balance these principles differently depending on whether the system needs cleaner reuse, fewer coordinated releases, or more localized change.
Component Coupling
The next principles govern the relationships between components rather than their internal makeup:
ADP: Acyclic Dependencies Principle
Avoid cycles in the component dependency graph.
The graph should stay directed and acyclic. When cycles appear, teams usually break them by introducing an abstraction and inverting dependencies.
SDP: Stable Dependencies Principle
Depend in the direction of stability.
Fan-in and Fan-out make that visible: more incoming dependencies and fewer outgoing ones usually mean a more stable component. I = Fan-out / (Fan-in + Fan-out) gives a compact stability signal.
SAP: Stable Abstractions Principle
A component should be as abstract as it is stable.
A = Na / Nc measures how abstract a component is. Together with SDP, this principle brings dependency inversion to the component level.
Main Sequence and risk zones
Ideal diagonal: a balance between abstractness and stability. Formula: D = |A + I - 1|
Concrete and stable components (A≈0, I≈0). Hard to change because many dependencies rely on them.
Abstract and unstable components (A≈1, I≈1). Abstractions that are weakly connected to real implementations.
Main architectural takeaway
Structure cannot be postponed
If architecture is always deferred, every next change becomes more expensive than it needs to be.
Plugin Architecture
Polymorphism and dependency inversion let stable policy stay in the center while replaceable details evolve around it.
Structure must evolve
Component boundaries are not designed once forever. They need to evolve as the product and its pressures change.
Main Sequence
Healthy components stay close to the main sequence instead of drifting into painful rigidity or useless abstraction.
Sources
Related chapters
- What Software Architecture Is and Why It Matters in System Design - provides the larger architecture frame where clean architecture becomes a system design concern rather than only an internal code concern.
- Fundamentals of Software Architecture (short summary) - extends the topic with architecture characteristics, styles, and system-level trade-offs.
- Software Requirements (short summary) - connects boundaries and dependencies to proper requirements discovery and scope prioritization.
- A Philosophy of Software Design (short summary) - broadens the perspective on complexity management and interface design in systems that need to stay maintainable.
- Decomposition strategies - translates clean architecture principles into practical service boundaries and responsibility split decisions.
- Architecture at Scale: How We Make Architectural Decisions - shows how to institutionalize decisions with RFC/ADR and manage architecture evolution across teams.