Hexagonal Architecture (Ports and Adapters)

Isolates application core from external systems. Core defines interfaces (ports), external systems provide implementations (adapters). Enables easy swapping of implementations and testing via mocks.

When to Use

• Application needs to be testable without real DB/email/external APIs
• Need to swap infrastructure (Postgres → MySQL, SendGrid → AWS SES)
• Multiple adapters for same port (REST + CLI + GraphQL)
• Business logic must be isolated from framework details

Don't use for:

• Simple CRUD with no testability requirements
• Scripts with single external dependency
• Prototypes