Hexagonal architecture: ports, adapters and semantic contracts

Cockburn’s Ports and Adapters isolates application logic from UI, database and other devices. Source dependencies point toward the application-owned ports, while runtime calls can travel outward through a driven port. The hexagon’s number of sides is not material, and replacing an adapter is not guaranteed to be a one-line DI change.

Что утверждает паттерн — и чего он не гарантирует

• Cockburn’s intent is an application runnable/testable without UI or database and connectable through adapters.
• Driving adapters invoke application ports; driven adapters implement ports owned by the application. Naming primary/secondary or inbound/outbound is secondary to the dependency boundary.
• Runtime control flow may point outward while source dependency remains inward through dependency inversion.
• Adapter replaceability is conditional on semantic contract and data migration, not guaranteed by interface syntax.

Границы и компоненты

Сценарии

Drive one use case through two adapters

HTTP and CLI normalize input into the same application command; transport-specific authentication and rendering stay outside the core.

Проверяемый исход: The core behavior is testable without a web server, and adapters cannot silently invent different business rules.

Persist through an application-owned port

The core asks for compare-and-set persistence semantics. The Postgres adapter implements the port and maps conflicts explicitly.

Проверяемый исход: The core never receives ORM rows; concurrency and transaction behavior are part of the port contract.

Handle an ambiguous payment outcome

The core supplies a stable idempotency key. A timeout after provider acceptance is unknown, not a definite decline; adapter queries/reconciles before retrying effect.

Проверяемый исход: No duplicate charge is created merely because a socket timed out.

Swap a persistence adapter safely

A candidate adapter passes semantic contract tests, data migration/backfill and shadow comparison before routing changes. DI alone cannot preserve unsupported transactions or queries.

Проверяемый исход: Cutover is gated on capability, data and failure equivalence; rollback remains possible.

Failure, concurrency и evolution checklist

• Contract-test success, conflict, timeout, cancellation and retry semantics for every adapter.
• Do not leak transport DTO, ORM row or provider enum across a core boundary.
• Use stable idempotency identities and explicit unknown state for remote effects.
• Persist integration intent durably; an in-memory callback chain is not an outbox.

Метрики, units и допущения

• Port timeout, retry budget and idempotency retention use explicit milliseconds/seconds/days.
• Adapter capacity is measured end-to-end under the required semantic contract; interface conformance gives no throughput guarantee.
• Migration completeness uses counts/hashes/invariants by range plus observed shadow mismatch rate, not only a successful DI startup.

Числа здесь — размерностные формулы или явно помеченные учебные inputs. Паттерн архитектуры сам по себе не задаёт SLA, throughput, latency или fault tolerance.

Связанные темы

[CONCEPT]clean-architecture

[CONCEPT]onion-architecture

Первичные источники

• https://alistair.cockburn.us/hexagonal-architecture/
• https://alistaircockburn.com/Articles/Hexagonal-Architecture

Scope note

Hexagonal architecture is a structural pattern. It does not by itself provide transactions, durable messaging, idempotency, authorization, adapter equivalence or a zero-downtime migration.