playbook/outfitter-agents/plugins/outfitter/skills/architecture/references/common-patterns.md

Common Architecture Patterns

API Gateway

Single entry point for all client requests, handles routing, auth, rate limiting.

• Use when: Multiple backend services, need centralized auth/logging
• Options: Kong, AWS API Gateway, custom Nginx
• Tradeoffs: Single point of failure, added latency

Backends for Frontends (BFF)

Separate backend for each frontend type.

• Use when: Different clients need different data shapes
• Benefits: Optimized per-client, independent deployment
• Tradeoffs: Code duplication, more services to maintain

Circuit Breaker

Prevent cascading failures by failing fast when downstream unhealthy.

• Implementation: Track failure rate, open circuit after threshold, half-open to test recovery
• Libraries: Hystrix (Java), Polly (.NET), Resilience4j (Java), opossum (Node)

Saga Pattern

Manage distributed transactions across services.

Type	Description
Choreography	Services emit events, others listen and react
Orchestration	Central coordinator manages workflow

• Use when: Multi-service transaction, eventual consistency acceptable

Strangler Fig

Gradually migrate from legacy by routing new features to new system.

1. Route all traffic through proxy/facade
2. Build new features in new system
3. Gradually migrate existing features
4. Sunset legacy when complete