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Cross-Module Service Boundaries

Modular Monoliths & Microservices​

In systems containing multiple domains (e.g., orders, billing, inventory, notifications), direct cross-module coupling breaks boundary isolation:

❌ Violating Boundary:
OrderService.ts ──(imports concrete class)──> PaymentService.ts

✅ Proper Boundary:
OrderService.ts ──(imports interface)───────> IPaymentService.ts
                                                     ▲
                                                     │ (implements)
PaymentService.ts ───────────────────────────────────┘

Policy Requirements​

  • Cross-module dependencies must depend on explicit interfaces (e.g., IPaymentService or PaymentInterface) rather than concrete service or repository classes.
  • This allows individual modules to be mocked in tests and later extracted into independent microservices with minimal friction.
  • Enforced by rule ARCH-004.