Hexagonal architecture (ports and adapters)

Business logic in the middle defines interfaces (ports); databases, APIs and user interfaces plug in from outside as adapters.

The core says “I need to save an order” and “I need to charge a card”; adapters implement that with Postgres or a payment provider. Dependencies point inward, so the rules can be tested without a database and an adapter can be swapped. Clean architecture and onion architecture are close variants. The cost is more interfaces and mapping code, which simple CRUD apps do not repay.

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Related terms

DDD (domain-driven design): Designing software around the business’s own language and rules, with the code split where that language changes meaning.
Modular monolith: One deployable application split inside into modules with clear boundaries, each owning its data and using the others only through defined interfaces.
Anti-corruption layer (ACL): A translation layer between your model and a legacy or external system, so its data shapes and quirks do not leak into your code.

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