When operational constraints prevent a microservice approach, hexagonal architecture provides a way to structure and maintain large monolithic applications.
A pricing feature, initially hosted within a larger application for convenience, serves as a real-world example of a distinct domain that can be structured for future extraction.
The architecture is built on three layers with a strict dependency rule where outer layers (adapters) depend on inner layers (application, domain), but not the other way around.
By isolating business logic from external dependencies and treating internal subdomains as clients, this architecture makes it easier to extract features into separate microservices later.
The ArchUnit testing library can be used in a CI/CD pipeline to validate dependency rules and prevent violations of the hexagonal structure.
To create stricter boundaries than testing allows, Java's modularization system can enforce architectural constraints at compile time, preventing invalid dependencies entirely.
After eight months of use, the architecture has proven its value by promoting cleaner code and better structure, making it a recommended approach for complex projects.
Jobs that call for the skills explored in this talk.