How to Enforce Hexagonal Architecture Boundaries in PHP with CI Checks

A structured guide explains how to implement hexagonal architecture in PHP 8.4+ by organizing source code into three strict namespace layers: Domain, Application, and Infrastructure. The Domain layer sits at the core with no external dependencies, while Application holds use cases and port interfaces, and Infrastructure handles framework wiring and external adapters. Imports are only permitted to point inward — Domain imports nothing external, Application imports Domain, and Infrastructure can import all layers. A PSR-4 Composer mapping ties each namespace directly to its directory, making the architecture visible at a glance from any import statement. The approach also recommends encoding these import rules into CI checks so violations break the build automatically, removing reliance on developer discipline alone.