common-system-design

name	common-system-design
description	Universal architectural standards for robust, scalable systems. Use when designing new features, evaluating architecture, or resolving scalability concerns. (triggers: architecture, design, system, scalability)

System Design & Architecture Standards

Priority: P0 (FOUNDATIONAL)

Architectural Principles

• SoC: Divide into distinct sections per concern.
• SSOT: One source, reference elsewhere.
• Fail Fast: Fail visibly when errors occur.
• Graceful Degradation: Core functional even if secondary fails.

Modularity & Coupling

• High Cohesion: Related functionality in one module.
• Loose Coupling: Use interfaces for communication.
• DI: Inject dependencies, don't hardcode.

Common Patterns

• Layered: Presentation → Logic → Data.
• Event-Driven: Async communication between decoupled components.
• Clean/Hexagonal: Core logic independent of frameworks.
• Statelessness: Favor stateless for scaling/testing.

Distributed Systems

• CAP: Trade-off Consistency/Availability/Partition tolerance. See CAP & Consistency Patterns.
• Idempotency: Operations repeatable without side effects. See Idempotency Patterns.
• Circuit Breaker: Fail fast on failing services. See Resilience Patterns.
• Eventual Consistency: Design for async data sync. See CAP & Consistency Patterns.

Documentation & Evolution

• Design Docs: Write specs before major implementations.
• Versioning: Version APIs/schemas for backward compatibility.
• Extensibility: Use Strategy/Factory for future changes.

References

• Distributed Systems & CAP Theorem
• Resilience Patterns (Circuit Breaker, Bulkhead, Retry)

Anti-Patterns

• No god classes: Single Responsibility — one reason to change per module.
• No synchronous coupling: Prefer events or queues for cross-service calls.
• No premature abstraction: Design for current load; scale when proven needed.