Software Architecture Rules

Design Principles

• Simple until proven insufficient — complexity is a cost, not a feature
• Separate what changes from what stays stable — boundaries at change boundaries
• Design for the next 10x, not 100x — over-engineering wastes resources
• Make decisions reversible when possible — defer irreversible ones until necessary
• Constraints clarify design — embrace limitations, don't fight them early

System Boundaries

• Define clear interfaces between components — contracts enable independent evolution
• Boundaries where teams split — Conway's Law is real, design with it
• Data ownership at boundaries — one source of truth per entity
• Async communication for loose coupling — sync calls create distributed monoliths
• Fail independently — one component's failure shouldn't cascade