2nd/10_Wiki/Topics/Architecture/비기능 요구사항 (Non-functional Requirements).md

---
id: wiki-2026-0508-비기능-요구사항-non-functional-requirem
title: 비기능 요구사항 (Non-functional Requirements)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [NFR, Non-functional Requirements, Quality Attributes, -ilities]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [architecture, requirements, quality-attributes, nfr, sre]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: YAML/SQL
  framework: SLO frameworks (Google SRE)
---

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

## 💻 패턴

### NFR specification (FURPS+)
```yaml
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)
```yaml
- 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
```yaml
# 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)
```javascript
// 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
```typescript
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;
    }
  }
}
```

### Accessibility audit (a11y NFR)
```typescript
// 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 |