Hexagonal architecture

Hexagonal architecture places domain and application policy at the center, exposing ports (interfaces) that adapters implement for HTTP, databases, queues, and UI. Inbound adapters drive use cases; outbound adapters satisfy driven ports. The metaphor reinforces testability by swapping edges without rewriting core rules.

On interviews: sketch primary and secondary adapters for a payment flow. Relate ports to interfaces in your stack and adapters to framework glue.

Common pitfalls: anemic hexagon with empty domain; ports that mirror framework controllers one-to-one; adapters containing business rules.

The trade-off is flexibility versus complexity—know when the simpler path is enough.

Checklist:

• Domain free of framework imports.
• Each external system has dedicated adapter.
• Use cases depend on outbound port interfaces.
• Contract tests on adapter boundaries.