---
id: mobile-crash-free-slo
title: Crash-free SLO — 99.5% 유지하기
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [mobile, crash, slo, reliability, vibe-coding]
tech_stack: { language: "Swift / Kotlin / RN", applicable_to: ["iOS", "Android"] }
applied_in: []
aliases: [crash-free, crashlytics SLO, ANR rate, mean time to detect, MTTD]
---

# Crash-free SLO

> Crash-free users 99.5%+ 가 산업 표준. **측정 + 알람 + 빠른 hotfix 채널**. iOS / Android 별 다름. **Crashlytics velocity alert** 자동.

## 📖 핵심 개념
- Crash-free users: 24h 동안 crash 안 본 사용자 비율.
- Crash-free sessions: 한 세션 안 crash 없음 비율.
- Velocity: 짧은 시간 내 빠른 증가 = 즉각 알람.
- ANR rate (Android): 별도 SLO.

## 💻 코드 패턴

### Crashlytics velocity alert
```
Firebase Console → Crashlytics → Velocity Alerts
- Threshold: 1% sessions affected
- Window: 1 hour
- Slack / email integration
```

### Sentry release health
```ts
// 앱 시작 시
Sentry.init({
  dsn,
  release: `app@${version}+${build}`,
  environment: 'prod',
  tracesSampleRate: 0.1,
  enableAutoSessionTracking: true,
});
```

```
Sentry Dashboard → Releases → Crash-free users / sessions
```

### SLO 정의
```yaml
SLO:
  crash_free_users_30d: 99.5%
  crash_free_sessions_30d: 99.8%
  ANR_rate_24h: < 0.47% (Play Console 표준)
  startup_latency_p95: < 2s

Alerts:
  - velocity > 1% in 1h → page oncall
  - daily crash-free < 99% → page
  - new crash signature affecting > 50 users / 1h → page
```

### 디버그 정보
```ts
Crashlytics.crashlytics().setUserID(user.id);
Crashlytics.crashlytics().setCustomValue(plan, forKey: 'plan');
Crashlytics.crashlytics().setCustomValue(experimentVariant, forKey: 'exp:onboarding');
Crashlytics.crashlytics().log("entered checkout flow")
```

### Symbol 업로드 자동
```
Fastlane: upload_symbols_to_crashlytics
또는 build script
```

dSYM 누락 = crash 의미 없음.

### Hotfix 채널
- iOS: TestFlight + 빠른 review (24h) + phased release pause.
- Android: Play Console internal testing → staged rollout 5% → full.

```ruby
# Fastlane: emergency hotfix 자동
lane :hotfix do
  ensure_git_branch(branch: 'hotfix/.*')
  match
  build_app
  upload_to_testflight(distribute_external: true, groups: ['Beta'])
end
```

### Phased release / staged rollout
```ruby
# iOS: App Store Connect API
upload_to_app_store(
  phased_release: true,  # 7일 자동 분배
)

# Android
upload_to_play_store(track: 'production', rollout: '0.05')
```

새 버전 issue 발견 → halt rollout.

### Kill switch (서버 제어 강제)
```ts
// 앱 시작 시 remote config
const config = await fetchRemoteConfig();
if (config.minSupportedBuild > currentBuild) {
  showUpdateRequiredScreen();
  return;
}
if (config.killFeature.checkout) {
  // checkout 비활성
}
```

### Client error rate (non-crash)
```ts
class GlobalErrorBoundary extends React.Component {
  componentDidCatch(error: Error, info: ErrorInfo) {
    Sentry.captureException(error, { extra: info });
    this.setState({ hasError: true });
  }
}
```

```ts
// JS unhandled rejection
window.addEventListener('unhandledrejection', (e) => {
  Sentry.captureException(e.reason);
});
```

### Postmortem 템플릿
```markdown
# Crash spike 2026-05-09
- Affected: 23,000 users (3.4%)
- Window: 14:00 - 15:30 UTC
- Root cause: 새 endpoint 의 nil response → force unwrap
- Fix: optional unwrap + fallback
- Hotfix: 1.4.2 (3 hours)
- Prevention: 빌드 시 force-unwrap lint 활성, integration test 추가
```

## 🤔 의사결정 기준
| 모니터 | 도구 |
|---|---|
| 일반 SLO | Crashlytics + Sentry |
| ANR (Android) | Crashlytics + Play Console |
| 시작 latency | Firebase Performance / SwiftUI Instruments |
| 메모리 / 배터리 | MetricKit (iOS) / Battery Historian (Android) |
| 네트워크 에러 | 자체 + Sentry breadcrumbs |
| User journey crash 영향 | Mixpanel / Amplitude |

## ❌ 안티패턴
- **dSYM / mapping 누락**: stack 의미 없음.
- **Crash velocity 알람 없음**: 큰 spike 모름.
- **Force unwrap (`!`) 무절제 (Swift)**: nil 시 crash. 옵션 unwrap.
- **Catch 후 swallow + continue**: 더 큰 crash. 또는 record + degrade.
- **Phased release 없음 prod**: 큰 영향 즉시.
- **Kill switch 없음**: emergency 시 review 기다림.
- **PII crash log 그대로**: GDPR. 마스킹.
- **Old version 무한 지원**: minSupportedBuild + 강제 update.

## 🤖 LLM 활용 힌트
- Crashlytics + Sentry 양쪽 권장 (각 강점 다름).
- Velocity alert + dSYM 자동 + phased release.
- Kill switch 로 emergency 대응.

## 🔗 관련 문서
- [[Native_Crash_Reporting]]
- [[Mobile_CI_CD_Fastlane]]
- [[Native_ANR_Freeze_Debugging]]
