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title

비기능 요구사항 (Non-functional Requirements, NFRs)

매 한 줄

"매 NFR은 시스템이 어떻게 동작해야 하는가의 명세이며 매 architecture는 NFR 의 함수다". 매 functional requirement 가 what 이라면 NFR 은 how-well; 매 ISO 25010 quality model 이 2026 의 표준이며 매 SLO/SLI 형태로 measurable 화 된다.

매 핵심

매 ISO/IEC 25010 quality attributes

Performance efficiency: time behaviour, resource utilization, capacity.
Reliability: availability, fault tolerance, recoverability, maturity.
Security: confidentiality, integrity, non-repudiation, authenticity, accountability.
Maintainability: modularity, reusability, analyzability, modifiability, testability.
Portability: adaptability, installability, replaceability.
Compatibility: co-existence, interoperability.
Usability: learnability, operability, accessibility.
Functional suitability: completeness, correctness, appropriateness.

매 measurable 화

SLI: 매 service-level indicator (latency p99, error rate, availability ratio).
SLO: 매 service-level objective (99.9% over 30d, p99 < 250ms).
SLA: 매 contract with consequences (penalty, refund).
Error budget: 매 1 - SLO; 매 deploy/feature freeze trigger.

매 응용

매 NFR-driven architecture: cache for performance, replication for availability, audit log for accountability.
매 NFR-driven test: load test, chaos engineering, security pentest, accessibility audit.
매 NFR-driven trade-off: CAP theorem (consistency vs availability), latency vs throughput.

💻 패턴

NFR specification (FURPS+)

nfr:
  performance:
    latency_p99_ms: 250
    throughput_rps: 1000
    cpu_utilization_max: 0.7
  availability:
    slo: 99.95
    measurement_window: 30d
    error_budget_min_per_quarter: 0.001
  security:
    auth: OAuth2 + PKCE
    transport: TLS 1.3 only
    data_at_rest: AES-256-GCM
    audit_log_retention: 7y
  scalability:
    horizontal: 10x peak in 5min
  observability:
    log_format: JSON, OpenTelemetry
    trace_sampling: 0.1

SLO definition (Prometheus)

- alert: APILatencyBudgetBurn
  expr: |
    (
      histogram_quantile(0.99,
        sum(rate(http_request_duration_seconds_bucket{job="api"}[5m])) by (le))
      > 0.25
    )
  for: 10m
  annotations:
    summary: p99 latency exceeds 250ms SLO

Multi-burn-rate alert

# Google SRE multi-window multi-burn-rate
- alert: ErrorBudgetFastBurn
  expr: |
    (
      sum(rate(http_requests_total{status=~"5.."}[1h]))
      / sum(rate(http_requests_total[1h]))
    ) > (14.4 * (1 - 0.999))
    AND
    (
      sum(rate(http_requests_total{status=~"5.."}[5m]))
      / sum(rate(http_requests_total[5m]))
    ) > (14.4 * (1 - 0.999))

Performance budget (frontend)

// budget.config.js — Lighthouse CI
module.exports = {
  ci: {
    assert: {
      assertions: {
        'first-contentful-paint': ['error', { maxNumericValue: 1800 }],
        'largest-contentful-paint': ['error', { maxNumericValue: 2500 }],
        'total-blocking-time':     ['error', { maxNumericValue: 200 }],
        'cumulative-layout-shift': ['error', { maxNumericValue: 0.1 }],
      },
    },
  },
};

Resilience: circuit breaker

class CircuitBreaker<T> {
  private failures = 0;
  private state: 'closed'|'open'|'half-open' = 'closed';
  private openedAt = 0;
  constructor(private fn: () => Promise<T>, private threshold = 5, private cooldownMs = 30_000) {}
  async call(): Promise<T> {
    if (this.state === 'open') {
      if (Date.now() - this.openedAt > this.cooldownMs) this.state = 'half-open';
      else throw new Error('circuit-open');
    }
    try {
      const r = await this.fn();
      this.failures = 0;
      this.state = 'closed';
      return r;
    } catch (e) {
      if (++this.failures >= this.threshold) {
        this.state = 'open';
        this.openedAt = Date.now();
      }
      throw e;
    }
  }
}

// axe-core CI gate
import { AxePuppeteer } from '@axe-core/puppeteer';
const results = await new AxePuppeteer(page).analyze();
const critical = results.violations.filter(v => v.impact === 'critical');
if (critical.length > 0) throw new Error(`a11y: ${critical.length} critical violations`);

매 결정 기준

상황	Approach
Public API	Latency + availability SLO + rate limit
Financial system	Strong consistency + audit log + 7y retention
Mobile app	Battery + bundle size + offline-first
B2B SaaS	Multi-tenant isolation + SOC2 + 99.9% SLA
Real-time game	p99 latency + tick budget + recoverability

기본값: 매 SMART NFR (Specific, Measurable, Achievable, Relevant, Time-bounded) + SLO 형태로 명세.

🔗 Graph

부모: Software Architecture
응용: ATAM (Architecture Trade-offs Analysis Method) · 소프트웨어 아키텍처 평가 (Software Architecture Evaluation)
Adjacent: SLO · Chaos Engineering · 복잡한 비즈니스 도메인 (금융 헬스케어 이커머스 등)

🤖 LLM 활용

언제: 매 NFR elicitation workshop, SLO/SLI draft, ISO 25010 mapping, NFR-to-architecture trace matrix. 언제 X: 매 binding SLA terms (legal review 필수), 매 actual production SLO measurement (instrumentation 필요).

❌ 안티패턴

Wishlist NFR: 매 "fast", "secure", "scalable" — non-measurable.
NFR as afterthought: 매 sprint 끝에 retrofit → architectural rewrite 발생.
One-size SLO: 매 모든 endpoint 99.99% → cost 폭증.
No error budget: 매 SLO 만 있고 budget consumption tracking 없음 → meaningless.
Gold-plating reliability: 매 needed 99.9% 위 99.999% pursuit → 100x cost.

🧪 검증 / 중복

Verified (ISO/IEC 25010:2023, Google SRE Book Ch.4, Bass et al. "Software Architecture in Practice" 4ed).
신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — ISO 25010 + SLO/SLI + NFR specification patterns

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