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-load-balancing-strategies
+title: Load Balancing Strategies
+category: 10_Wiki/Topics
+status: verified
+canonical_id: self
+aliases: [Load Balancer, LB, Reverse Proxy]
+duplicate_of: none
+source_trust_level: A
+confidence_score: 0.9
+verification_status: applied
+tags: [networking, load-balancer, nginx, envoy, haproxy, aws-alb]
+raw_sources: []
+last_reinforced: 2026-05-10
+github_commit: pending
+tech_stack: { language: Config, framework: Nginx/Envoy/HAProxy/AWS }
+---
+
+# Load Balancing Strategies
+
+## 매 한 줄
+> **"매 LB = traffic 분산 + health check + sticky"**. 알고리즘은 균등성과 affinity의 trade-off.
+
+## 매 핵심
+### 매 알고리즘
+- **Round-robin**: 순차. 단순, 동질 서버.
+- **Weighted RR**: 용량 차등.
+- **Least connections**: 활성 연결 최소. long-lived 적합.
+- **Least response time**: 평균 응답 + connection 수.
+- **IP hash**: client IP→server. session affinity.
+- **Consistent hash**: cache/shard. node 추가 시 K/n key만 재배치.
+- **Random / P2C**: power of two choices, least-loaded 선택. 간단·강력.
+
+### 매 Layer
+- **L4 (TCP/UDP)**: 빠름, opaque. NLB, HAProxy TCP mode.
+- **L7 (HTTP)**: header/path 기반 라우팅, TLS 종료. ALB, Nginx, Envoy.
+
+### 매 Health check
+- Active: /health 주기적 GET
+- Passive: 실제 요청 실패 카운트
+- Slow start: 신규 노드에 점진적 traffic
+- Outlier detection (Envoy): 연속 5xx → eject
+
+### 매 Session affinity (sticky)
+- Cookie-based (LB가 cookie 발급)
+- Source IP (NAT 뒤에 모이면 unbalanced)
+- Header-based (custom)
+
+### 매 응용
+1. Web app: ALB + multi-AZ
+2. gRPC/HTTP2: Envoy (L7 multiplex)
+3. DB read replica: ProxySQL, PgBouncer
+4. Cache shard: consistent hash (Redis cluster)
+5. Service mesh: Envoy sidecar (Istio, Linkerd)
+
+## 💻 패턴
+### Nginx upstream
+```nginx
+upstream backend {
+    least_conn;                    # algorithm
+    server app1:8080 weight=3 max_fails=3 fail_timeout=30s;
+    server app2:8080 weight=1;
+    server app3:8080 backup;       # only if others down
+    keepalive 32;
+}
+server {
+    location / {
+        proxy_pass http://backend;
+        proxy_set_header Host $host;
+        proxy_next_upstream error timeout http_502 http_503;
+    }
+}
+```
+
+### HAProxy
+```
+backend web
+    balance leastconn
+    option httpchk GET /health
+    server s1 10.0.0.1:8080 check weight 100
+    server s2 10.0.0.2:8080 check weight 50
+    cookie SRV insert indirect nocache    # sticky
+```
+
+### Envoy (L7, gRPC)
+```yaml
+clusters:
+- name: api
+  type: STRICT_DNS
+  lb_policy: LEAST_REQUEST
+  health_checks:
+  - timeout: 1s
+    interval: 5s
+    http_health_check: { path: "/health" }
+  outlier_detection:
+    consecutive_5xx: 5
+    base_ejection_time: 30s
+  load_assignment:
+    cluster_name: api
+    endpoints:
+    - lb_endpoints:
+      - endpoint: { address: { socket_address: { address: api1, port_value: 8080 }}}
+```
+
+### AWS ALB (Terraform)
+```hcl
+resource "aws_lb" "app" {
+  name               = "app-alb"
+  load_balancer_type = "application"
+  subnets            = var.public_subnets
+}
+resource "aws_lb_target_group" "api" {
+  port     = 8080
+  protocol = "HTTP"
+  health_check { path = "/health"; interval = 15 }
+  stickiness { type = "lb_cookie"; enabled = true }
+}
+```
+
+### Consistent hash (Python sketch)
+```python
+import bisect, hashlib
+class Ring:
+    def __init__(self, nodes, vnodes=150):
+        self.ring = []
+        for n in nodes:
+            for i in range(vnodes):
+                h = int(hashlib.md5(f"{n}-{i}".encode()).hexdigest(), 16)
+                bisect.insort(self.ring, (h, n))
+    def get(self, key):
+        h = int(hashlib.md5(key.encode()).hexdigest(), 16)
+        i = bisect.bisect(self.ring, (h, ""))
+        return self.ring[i % len(self.ring)][1]
+```
+
+### P2C (power of two choices)
+```python
+import random
+def p2c(servers, load):
+    a, b = random.sample(servers, 2)
+    return a if load[a] <= load[b] else b
+```
+
+## 매 결정 기준
+| 상황 | LB / 알고리즘 |
+|---|---|
+| AWS web app | ALB + round_robin |
+| TCP / 빠름 | NLB / HAProxy L4 |
+| gRPC, mesh | Envoy least_request |
+| Cache shard | Consistent hash |
+| DB connection pool | PgBouncer/ProxySQL |
+| Bare metal HTTP | Nginx least_conn |
+| 동질 서버 + short req | RR/Random |
+| 이질 서버 / long conn | Weighted least-conn |
+
+**기본값**: HTTP는 ALB or Nginx least_conn. 마이크로서비스는 Envoy.
+
+## 🔗 Graph
+- 부모: [[Distributed-Systems]]
+- 변형: [[Consistent-Hashing]], [[Reverse-Proxy]]
+- 응용: [[High-Availability]], [[Service Mesh]], [[CDN]]
+- Adjacent: [[API-Gateway]]
+
+## 🤖 LLM 활용
+**언제**: config 작성, 알고리즘 선택, troubleshoot 가설.
+**언제 X**: production tuning은 metric 기반 검증 필수.
+
+## ❌ 안티패턴
+- IP hash + NAT/CGNAT (모든 client가 한 노드)
+- Sticky session 과의존 → 노드 죽으면 세션 다 잃음
+- Health check 너무 짧은 interval → flapping
+- L7 LB에서 keepalive 비활성화 → 성능↓
+- Hash ring vnode 부족 → 불균형
+- TLS termination만 보고 backend mTLS 무시
+
+## 🧪 검증 / 중복
+- Verified (Nginx/Envoy/HAProxy docs, Mitzenmacher P2C, AWS ELB docs). 신뢰도 A.
+- 중복: 없음.
+
+## 🕓 Changelog
+| 날짜 | 변경 |
+|---|---|
+| 2026-05-08 | Phase 1 |
+| 2026-05-10 | Manual cleanup — Envoy/AWS/consistent-hash 코드 추가 |