Non-Functional Requirements
The quality attributes that define how well a system performs its functions
PerformanceResponse time targets, throughput, latency percentiles (P50 / P95 / P99)›ScalabilityVertical vs horizontal scaling, elasticity, auto-scaling strategies›AvailabilityUptime SLAs (99.9% ≈ 8.7 hr/yr · 99.99% ≈ 52 min/yr), redundancy models›ReliabilityFault tolerance, MTTR, MTBF, chaos engineering›SecurityAuthentication, authorization, encryption at rest and in transit, threat modeling›MaintainabilityModularity, testability, documentation, code quality metrics›ObservabilityStructured logging, metrics, distributed tracing — the three pillars›ComplianceGDPR, HIPAA, PCI-DSS, SOC 2, ISO 27001, data residency requirements›Cost EfficiencyFinOps principles, TCO analysis, reserved vs spot capacity, rightsizing›Disaster RecoveryRTO, RPO, backup and restore strategies, failover planning›InteroperabilityAPI contracts, backward compatibility, integration standards›PortabilityCloud-agnostic design, avoiding vendor lock-in, containerization›NFR PrioritizationBalancing competing requirements, trade-off matrices, stakeholder alignment›