Hexagonal Architecture is Not a Layered Architecture: Topology, Safety, and When to Walk Away

Most introductory articles draw it as an onion Every article about Hexagonal Architecture ends up with the same diagram: three concentric circles. Domain on the inside, Application in the middle, Infrastructure on the outside. Onion Architecture. Clean Architecture. Layered Architecture with a different hat. This is not what Ports & Adapters is. The difference is not in the number of layers—it's in the direction of coupling . In a layered architecture, dependency flows vertically: Controller