Architectural Styles: Selection and Trade-offs

Style Selection Decision Tree

Start here. Answer the dominant driver, follow to recommended style.

Is the domain complex with rich business rules?
  YES -> Do you need infrastructure independence and high testability?
    YES -> Hexagonal / Clean / Onion (functionally equivalent, different terminology)
    NO  -> Is the domain well-understood with clear module boundaries?
      YES -> Modular Monolith (single deployment, structured boundaries)
      NO  -> Layered Architecture (simple, well-known, fast to start)
  NO -> Is this a feature-heavy application with independent feature teams?
    YES -> Vertical Slice (per-feature organization, CQRS-friendly)
    NO  -> Do you need independent deployment and scaling per capability?
      YES -> Can the team handle distributed system operational complexity?
        YES -> Microservices
        NO  -> Modular Monolith (extract to services later)
      NO  -> Is the primary concern async workflows or event-driven processing?
        YES -> Event-Driven Architecture
        NO  -> Is this a data processing pipeline?
          YES -> Pipe and Filter
          NO  -> Layered Architecture (sensible default)

Cross-Cutting Comparison Matrix