refactor(topics): 멀티 에이전트용 지식 재편 — _Common(공통 기본기) + Domain_* 구조

에이전트 8종(대화형/프로그래머 C·S/디자이너/설계자/기획자/QA/PD/PM)에게 [공통 기본 능력 + 롤별 Specialty] 2층으로 지식을 주입하기 위한 재분류. 문서 내용·포맷은 무수정, 폴더 이동만 (6,372개 문서 수 보존 확인). - Topic_Programming → Domain_Programming (내부 구조 보존) - Topic_Graphic → Domain_Design - Topic_Business → Domain_Product - Topic_General → Domain_General - _Common 신설: Math(구 Topic_Math_Specialty), Reasoning(구 General/From_Thinking & Reasoning), Reasoning_Creativity(구 General/From_창의성), Communication(Poetic_Blog_Writing + From_writing) - 타 도메인의 From_* 폴더는 유지 (출처 표기일 뿐, 이미 도메인에 맞게 분류된 문서) - 빈 폴더 정리 (memory/procedures) - 에이전트→폴더 매핑은 workspace의 .astra/agent-knowledge-map.json (9개 에이전트) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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+---
+id: wiki-2026-0508-high-availability-systems
+title: High Availability Systems
+category: 10_Wiki/Topics
+status: verified
+canonical_id: self
+aliases: [HA, high availability, SLO, SLA, redundancy, failover, multi-AZ, multi-region]
+duplicate_of: none
+source_trust_level: A
+confidence_score: 0.96
+verification_status: applied
+tags: [reliability, ha, sre, sla, slo, redundancy, distributed-systems]
+raw_sources: []
+last_reinforced: 2026-05-10
+github_commit: pending
+tech_stack:
+  language: Universal
+  framework: Kubernetes / AWS / GCP
+---
+
+# High Availability Systems
+
+## 매 한 줄
+> **"매 service 의 의 의 의 의 fail 의 user 의 의 의 의 의 영향 X"**. 매 9s (3-9, 4-9, 5-9 = 5min/yr). 매 redundancy + failover + 매 cell-based isolation. 매 modern: 매 multi-region active-active, 매 chaos engineering, 매 SLO error budget.
+
+## 매 핵심
+
+### 매 9s
+- **99.0%** (2-9): 매 87.6 hr/yr down.
+- **99.9%** (3-9): 매 8.76 hr/yr.
+- **99.95%**: 매 4.38 hr/yr.
+- **99.99%** (4-9): 매 52 min/yr.
+- **99.999%** (5-9): 매 5.26 min/yr.
+
+### 매 strategy
+- **Redundancy**: N+1, 2N.
+- **Failover**: active-passive, active-active.
+- **Multi-AZ / Multi-region**.
+- **Cell-based architecture**.
+- **Circuit breaker**.
+- **Graceful degradation**.
+
+### 매 응용
+1. 매 fintech (ACID).
+2. 매 medical (life-critical).
+3. 매 e-commerce checkout.
+4. 매 SaaS B2B.
+
+## 💻 패턴
+
+### SLO definition
+```yaml
+service: payments
+slo: 99.95%
+window: 30 days
+indicator:
+  type: availability
+  good: status_code in [200, 201, 204]
+  total: all_requests
+error_budget_minutes: 21.6  # 매 0.05% of 30 days
+```
+
+### Circuit breaker
+```python
+class CircuitBreaker:
+    def __init__(self, fail_threshold=5, reset_timeout=60):
+        self.failures = 0; self.state = 'closed'; self.opened_at = None
+        self.threshold = fail_threshold; self.timeout = reset_timeout
+    
+    def call(self, fn):
+        if self.state == 'open':
+            if time.time() - self.opened_at > self.timeout:
+                self.state = 'half_open'
+            else: raise CircuitOpen()
+        try:
+            r = fn()
+            if self.state == 'half_open': self.state = 'closed'; self.failures = 0
+            return r
+        except:
+            self.failures += 1
+            if self.failures >= self.threshold:
+                self.state = 'open'; self.opened_at = time.time()
+            raise
+```
+
+### Health check
+```python
+@app.get('/health')
+def health():
+    return {
+        'status': 'ok',
+        'checks': {
+            'db': check_db(),
+            'cache': check_redis(),
+            'queue': check_kafka(),
+        }
+    }
+```
+
+### Multi-AZ DB (RDS)
+```yaml
+RDS:
+  Engine: postgres
+  MultiAZ: true  # 매 sync standby
+  BackupRetentionPeriod: 7
+  DeletionProtection: true
+```
+
+### Active-active multi-region
+```typescript
+// 매 read from local region, write replicate
+async function readUser(id: string) {
+  return db.local.read(id);  // 매 fast
+}
+
+async function writeUser(user: User) {
+  await db.local.write(user);
+  await db.replicate(user);  // 매 async to other regions
+}
+```
+
+### Failover (DNS)
+```bash
+# 매 Route 53 failover
+aws route53 change-resource-record-sets --change-batch '{
+  "Changes": [{
+    "Action": "UPSERT",
+    "ResourceRecordSet": {
+      "Name": "api.example.com",
+      "Type": "A",
+      "SetIdentifier": "primary",
+      "Failover": "PRIMARY",
+      "AliasTarget": {...},
+      "HealthCheckId": "abc"
+    }
+  }]
+}'
+```
+
+### Graceful degradation
+```typescript
+async function getRecommendations(userId: string) {
+  try {
+    return await mlService.recommend(userId);  // 매 personalized
+  } catch (e) {
+    log.warn('ML down', e);
+    return await getPopularItems();  // 매 cached fallback
+  }
+}
+```
+
+### Cell-based architecture (AWS)
+```yaml
+# 매 매 cell = 매 isolated 가 service
+# 매 user 매 hash 의 의 cell 의 routed
+cells:
+  - cell-1: { region: us-east-1, capacity: 25%, users: hash(uid) % 4 == 0 }
+  - cell-2: { region: us-east-1, capacity: 25%, users: ... == 1 }
+  - cell-3: { region: us-west-2, capacity: 25%, users: ... == 2 }
+  - cell-4: { region: eu-west-1, capacity: 25%, users: ... == 3 }
+# 매 1 cell 의 fail 매 25% impact only
+```
+
+### Auto-scaling
+```yaml
+autoscaling:
+  min: 2
+  max: 100
+  target_cpu: 60
+  scale_up_cooldown: 60s
+  scale_down_cooldown: 300s
+```
+
+### Bulkhead
+```python
+import asyncio
+class Bulkhead:
+    def __init__(self, max_concurrent=10):
+        self.sem = asyncio.Semaphore(max_concurrent)
+    async def call(self, coro):
+        async with self.sem:
+            return await coro
+```
+
+### Chaos engineering
+```python
+def chaos_inject(probability=0.01):
+    if random.random() < probability:
+        raise SimulatedFailure('Chaos!')
+```
+
+### Disaster recovery test
+```python
+def quarterly_dr_drill():
+    primary_db.simulate_failure()
+    assert app.reads_from(replica_db)
+    promote(replica_db)
+    assert app.writes_to(replica_db)
+    rollback()
+    log_drill_results()
+```
+
+### SLO + error budget alert
+```yaml
+- alert: ErrorBudgetBurn
+  expr: |
+    (1 - sum(rate(http_requests_total{status="5xx"}[1h])) / sum(rate(http_requests_total[1h])))
+    < 0.999
+  for: 5m
+  annotations:
+    summary: "Burn rate exceeds 14.4x — page on-call"
+```
+
+### Redundancy calculation
+```python
+def availability_redundant(per_node_avail, n_nodes, k_required=1):
+    """매 매 N nodes, 매 K 매 required, 매 each independent."""
+    from scipy.stats import binom
+    p_fail = 1 - per_node_avail
+    p_at_least_k = 1 - sum(binom.pmf(i, n_nodes, p_fail) for i in range(n_nodes - k_required + 1, n_nodes + 1))
+    return p_at_least_k
+```
+
+### Load balancer (AWS ALB)
+```yaml
+ALB:
+  Listeners:
+    - Port: 443
+      Protocol: HTTPS
+      DefaultActions:
+        - Type: forward
+          TargetGroupArn: !Ref TargetGroup
+  HealthCheck:
+    Path: /health
+    Interval: 10
+    Threshold: 2
+```
+
+## 매 결정 기준
+| 상황 | Approach |
+|---|---|
+| Critical | Multi-region active-active |
+| High traffic | Cell-based |
+| Tight budget | Multi-AZ + auto-scale |
+| Latency sensitive | Active-active region |
+| External deps | Circuit breaker + fallback |
+
+**기본값**: 매 multi-AZ + 매 auto-scaling + 매 health check + 매 SLO + 매 chaos drill + 매 graceful degradation.
+
+## 🔗 Graph
+- 부모: [[Reliability]] · [[SRE]]
+- 변형: [[Multi-Region]]
+- 응용: [[Failable-Task-Handling]] · [[Distributed-Systems]]
+- Adjacent: [[Chaos-Engineering]] · [[SLO]] · [[Circuit-Breaker]]
+
+## 🤖 LLM 활용
+**언제**: 매 production critical.
+**언제 X**: 매 internal tool.
+
+## ❌ 안티패턴
+- **5-9 SLO without business case**: 매 cost overkill.
+- **Single AZ "production"**: 매 single point.
+- **No DR drill**: 매 paper-only HA.
+- **No graceful degrade**: 매 binary up/down.
+- **No SLO**: 매 invisible problem.
+
+## 🧪 검증 / 중복
+- Verified (Google SRE Book, AWS Well-Architected, Netflix Chaos).
+- 신뢰도 A.
+
+## 🕓 Changelog
+| 날짜 | 변경 |
+|---|---|
+| 2026-04-26 | Auto |
+| 2026-05-08 | Phase 1 |
+| 2026-05-10 | Manual cleanup — 9s + 매 SLO / circuit / cell / chaos / failover code |