Often, software engineers ask themselves what the most efficient solution to a problem is. As these problems roll through, they stamp each with an appropriate solution—this, they tell themselves, is the job of a programmer. Their solutions coalesce into bundles and packages, shoved down subdirectories of subdirectories, labeled and nested in an ever-growing labyrinth of code. The most efficient way to organize their solutions; this is architecture.
Software architecture is often overlooked by solo developers and small startup teams because, by its nature, it is most relevant to larger organizations. However, every small organization has dreams and fantasies of becoming a larger one. These dreams often collapse under the reality of their toppling codebases—systems built on foundations of patchwork example code, missing abstractions, and circular dependencies that no one planned for.
From Problems to Requirements and Features
In the realm of software engineering, those problems are often called requirements…
The path from business problems to concrete architecture runs through requirements, specifications, and features.
Test-Driven Development and Specifications
Test-Driven Development is a key element of Agile practices, and writing the technical specifications for a project is the first step toward producing a suite of adequate unit tests. The process of TDD is to first create the project in its entirety but keep class and function implementations empty so that the project can compile while every test fails. This enables developers to isolate and resolve environmental errors before touching application logic. Implementation can then proceed module by module; each paired with its corresponding tests. This ensures the implemented design adheres to the written specifications and that the software fulfills its requirements as intended. The efficacy of the system at this stage depends heavily on the breadth and quality of its test coverage.
A software’s architecture can vary wildly depending on the paradigms, languages, frameworks, and implementation details relevant to the requirements. There are often multiple tools capable of addressing the same need, and choosing among them can drastically influence how the system evolves. Across these varied ecosystems, common design patterns emerge—event-driven systems, peer-to-peer systems, layered architectures, microservices, pipelines. These patterns aren’t just theoretical constructs; they are the crystallized wisdom of decades of practice. They define how data structures and algorithms interact within a project and how those interactions expand into systems capable of meeting real-world requirements.
TDD uses specifications to drive tests, which drive implementation and refactoring.
Robert C. Martin’s Clean Architecture
Robert C. Martin’s Clean Architecture offers one of the clearest blueprints for building scalable, maintainable, enterprise-grade systems. What makes an architecture “clean”? Every software system has external dependencies—frameworks, technology stacks, OS quirks, third-party services—and it also has an internal dependency structure binding its own modules together. When organizing software, it’s essential to understand which parts of the system will change, why they will change, and how often that change will occur. Anticipating how software might evolve is the cornerstone of future-proof design.
Martin uses the idea of stability to describe how likely a module is to change based on its dependencies. Clean architecture, then, aims to maximize stability where stability matters and isolate unstable components behind interfaces where volatility is unavoidable. The result is a system whose most valuable and durable logic is shielded from the chaos of changing requirements, shifting technologies, and runtime environments. This concept is more intuitive in terms of software updates. The frameworks and libraries relied on all update on different schedules and developers subtly recognize the repercussion of those changes as bugs crop up in their codebase; meanwhile the next changes are being deployed. The entire foundation of Martin's philosophy of software architecture is to separate the core business logic from the dynamic and unstable environment that the infrastructure dependencies live inside.
The Four Layers of Clean Architecture
Clean Architecture defines four functional layers…
Clean Architecture layers: the application layer bridges the stable domain and volatile infrastructure.
Clean Architecture defines four functional layers that software components can be organized into. The domain layer contains the core business logic; entities, data structures/types, and the interfaces for services used throughout the application. This layer is the most stable portion of the software. It represents the pure, platform-independent definition of the problem being solved and the rules that must always hold true. It is intentionally insulated from external frameworks and technologies. Under ideal circumstances, the domain layer should only change when the fundamental nature of the system’s requirements changes, not when infrastructure or tools evolve.
The infrastructure layer contains the concrete implementation of required third-party technologies. This typically includes databases, mathematical libraries, rendering engines, communication protocols, storage systems, and other operational dependencies. Because these technologies evolve rapidly, this layer is inherently unstable. For this reason, the infrastructure layer commonly implements interfaces defined in the domain layer. Doing so allows external frameworks to be wrapped in domain-compatible types, insulating the rest of the application from changes occurring in external libraries or vendor ecosystems.
The application layer is the true bridge between the stable domain layer and the dynamic infrastructure layer. It orchestrates the domain’s rules using the capabilities provided by the infrastructure. The application layer integrates these two worlds by coordinating workflows, enforcing business processes, sequencing operations, and ensuring that domain logic is executed correctly using real technologies. Where the domain layer defines what must be done, and the infrastructure layer defines how each operation is technically carried out, the application layer defines how those rules and tools interact to fulfill real features.
The interface layer is responsible for exposing the features implemented in the application layer to the end user or external systems. In an API, this means routes, controllers, serializers, and protocol handling. In a GUI application, this layer may consist of UI components, input events, rendering logic, or user interaction workflows. Its job is to convert user or system inputs into structures the application layer understands, and to convert outputs back into a form suitable for external consumption.
This division of functional components within an application is a tried-and-tested architectural strategy that separates concerns based on stability and iterability. By isolating the volatile infrastructure from the stable domain logic through the mediating application layer, the system becomes more maintainable, more adaptable, and far more resistant to the long-term accumulation of technical debt. This layered approach allows a codebase to scale sustainably without collapsing under the stress of evolving tools, frameworks, and requirements.