Example 1 EXECUTIVE SUMMARY System Overview: PayFlow is a digital wallet and peer-to-peer payment platform. Business Objectives: Secure financial transactions at scale. Recommended API Style: REST + Event-Driven Architecture Key Architectural Decisions: - REST for client APIs - Event-driven transaction processing - OAuth 2.0 authentication - Redis caching # API STRATEGY Public APIs: - Wallet API - Payment API Internal APIs: - Fraud API - Ledger API Recommendation: REST for public consumers. Event-driven messaging for transaction processing. # DOMAIN MODELING Core Entities: - User - Wallet - Transaction Relationships: User → Wallet Wallet → Transaction Aggregate Root: Wallet # API RESOURCE DESIGN Resource: Wallet Purpose: Store balances and transaction history. Lifecycle: Created → Active → Suspended → Closed # ENDPOINT DESIGN POST /wallets Purpose: Create wallet. Authentication: OAuth 2.0 Status Codes: 201, 400, 401 # ARCHITECTURE DECISION RECORD Decision: REST API Alternatives: GraphQL Pros: Simple, cacheable. Cons: More endpoints. Reason Selected: Strong ecosystem and operational simplicity. Confidence: High # TRADE-OFF ANALYSIS MATRIX REST vs GraphQL Scalability: Winner: REST Developer Flexibility: Winner: GraphQL Recommendation: REST # AUTHENTICATION & AUTHORIZATION Authentication: OAuth 2.0 + JWT Authorization: RBAC Roles: User, Admin, Support # VERSIONING STRATEGY Method: URI Versioning Example: v1/payments Deprecation: 12-month support period # SECURITY REVIEW Risk: Fraudulent Transactions Severity: Critical Mitigation: Transaction signing Audit logging # RATE LIMITING User: 100 requests/min Partner: 1000 requests/min # ERROR ARCHITECTURE Error Format: { code, message, correlation_id } # SCALABILITY STRATEGY Caching: Redis Pagination: Cursor-based Async Processing: Transaction queue # PERFORMANCE ANALYSIS Latency Target: <200ms Bottleneck: Fraud scoring service Mitigation: Async evaluation # EVENT ARCHITECTURE Events: PaymentCreated PaymentCompleted Retry: Exponential backoff DLQ: Enabled # OBSERVABILITY STRATEGY Metrics: Latency Error Rate Tracing: Distributed tracing # DOCUMENTATION STRATEGY Standard: OpenAPI 3.1 SDK: JavaScript, Python # TESTING STRATEGY Unit Tests: Required Integration Tests: Required Load Tests: Required # API GOVERNANCE Naming: Consistent resource naming Ownership: Service ownership defined # COST OPTIMIZATION High Impact: Reduce excessive API polling # DEVELOPER EXPERIENCE REVIEW Learnability: 8/10 Documentation: 9/10 # API EVOLUTION ROADMAP MVP: Monolith Growth: Service decomposition Enterprise: Multi-region deployment # FAILURE MODE ANALYSIS Database Failure Impact: Transactions unavailable Recovery: Read replicas Automated failover # ANTI-PATTERN REVIEW Risk: Premature microservices Recommendation: Start modular monolith # PRODUCTION READINESS REVIEW Reliability: READY Security: READY WITH CHANGES Overall: READY WITH CHANGES # API REVIEW BOARD Principal Architect: Approved Security Engineer: Minor changes required Platform Engineer: Approved # API SCORECARD Design: 9.0 Security: 9.2 Scalability: 8.8 Performance: 8.7 Overall: 9.0/10 # FINAL RECOMMENDATION RECOMMENDED WITH MODIFICATIONS Reason: Strong architecture with minor security hardening required. # VALIDATION SUMMARY ✓ Resource Naming Consistency ✓ Endpoint Consistency ✓ Authentication Coverage ✓ Authorization Coverage ✓ Versioning Strategy ✓ Security Coverage ✓ Scalability Coverage ✓ Performance Coverage ✓ Governance Coverage ✓ Documentation Coverage ✓ Observability Coverage ✓ Operational Readiness ✓ Failure Recovery Coverage ✓ Production Readiness