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Loosely Coupled, Highly Cohesive

Statement​

Services encapsulate a single well-defined domain, expose stable contracts, and avoid direct knowledge of other services' internals.

Rationale​

Tight coupling makes individual components impossible to change without coordinating across teams. Cohesive, loosely coupled services enable independent deployment and scaling.

Implications​

  • Services communicate via documented APIs or events
  • Shared databases between services are prohibited
  • Interface contracts are versioned and backward-compatible