Vertical architecture VS Horizontal architecture #

✅ What is Layered Architecture? #

Layered architecture (also called n-tier architecture) organizes code into horizontal layers, where each layer has a specific role and communicates only with the layer directly below it.

Typical Layers: #

1. Presentation layer – UI or API layer (e.g. controllers).
2. Application layer – Coordinates use cases, handles application logic.
3. Domain layer – Business logic, entities, domain rules.
4. Infrastructure layer – External systems (DBs, APIs, files, etc).

📌 Direction of dependencies: Upper layers depend on lower ones (e.g., UI → Application → Domain → Infra).

✅ What is Horizontal Architecture? #

This usually refers to organizing code by feature or module, not by technical layer. Each module contains its own UI, business logic, and data access.

Example modules:

• orders/

  • controller.py, service.py, repository.py

• users/

  • controller.py, service.py, repository.py

📌 It’s also called feature-based, modular, or sometimes vertical slicing (opposite of horizontal layering).

✅ Clean Architecture Patterns: Horizontal or Layered? #

Clean Architecture (as proposed by Robert C. Martin) is technically a layered architecture, but with a twist: inversion of dependencies.

Clean Architecture Layers (from center out): #

• Entities (core domain)
• Use Cases / Interactors
• Interface Adapters (controllers, presenters, gateways)
• Frameworks & Drivers (web, DB, etc.)

But in Clean Architecture:

Dependencies must always point inward, toward the business rules.

So:

• Clean Architecture is layered.
• It’s not horizontal, because it organizes code by layers, not by feature.

🧭 Other Architectural Styles #

Here are some other major ones to know:

🧠 Summary #

Would you like a diagram comparing these visually?