---
id: devops-service-mesh-deep
title: Service Mesh — Istio / Linkerd / 트래픽 관리
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [devops, service-mesh, istio, linkerd, vibe-coding]
tech_stack: { language: "YAML / Istio / Linkerd", applicable_to: ["DevOps"] }
applied_in: []
aliases: [Istio, Linkerd, service mesh, sidecar, mTLS, traffic split, virtual service]
---

# Service Mesh

> Pod 옆 sidecar proxy (Envoy / linkerd2-proxy) 가 통신 가로챔. **mTLS 자동 / traffic split / retry / circuit breaker 코드 외부화**. **Linkerd = 가벼움, Istio = 풀 기능**.

## 📖 핵심 개념
- Sidecar: 매 pod 옆 proxy.
- Data plane: 실제 트래픽 처리.
- Control plane: 정책 배포 (Istiod, linkerd-controller).
- mTLS: 자동 - 모든 service 간 암호화 + 인증.

## 💻 코드 패턴

### Linkerd 설치
```bash
linkerd check --pre
linkerd install --crds | kubectl apply -f -
linkerd install | kubectl apply -f -
linkerd check
```

### Inject sidecar
```bash
kubectl get deploy api -o yaml | linkerd inject - | kubectl apply -f -

# 또는 namespace 자동
kubectl annotate ns prod linkerd.io/inject=enabled
```

### mTLS (자동)
```bash
linkerd viz edges deployment
# 모든 service 간 → mTLS
```

### Istio VirtualService (traffic split)
```yaml
apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata: { name: api }
spec:
  hosts: [api]
  http:
  - match: [{ headers: { x-canary: { exact: "true" } } }]
    route: [{ destination: { host: api, subset: v2 } }]
  - route:
    - { destination: { host: api, subset: v1 }, weight: 90 }
    - { destination: { host: api, subset: v2 }, weight: 10 }
```

```yaml
apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata: { name: api }
spec:
  host: api
  subsets:
  - name: v1
    labels: { version: v1 }
  - name: v2
    labels: { version: v2 }
```

→ 90/10 canary, header 가 있으면 100% v2.

### Retry / timeout
```yaml
apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata: { name: api }
spec:
  http:
  - route: [{ destination: { host: api } }]
    timeout: 5s
    retries:
      attempts: 3
      perTryTimeout: 2s
      retryOn: 5xx,reset,connect-failure
```

### Circuit breaker
```yaml
apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata: { name: api }
spec:
  host: api
  trafficPolicy:
    connectionPool:
      tcp: { maxConnections: 100 }
      http: { http2MaxRequests: 1000, maxRequestsPerConnection: 10 }
    outlierDetection:
      consecutive5xxErrors: 5
      interval: 30s
      baseEjectionTime: 30s
```

### AuthorizationPolicy
```yaml
apiVersion: security.istio.io/v1beta1
kind: AuthorizationPolicy
metadata: { name: api-allow }
spec:
  selector: { matchLabels: { app: api } }
  rules:
  - from:
    - source: { principals: ["cluster.local/ns/prod/sa/web"] }
    to:
    - operation: { methods: [GET, POST] }
```

### Linkerd traffic split (SMI)
```yaml
apiVersion: split.smi-spec.io/v1alpha1
kind: TrafficSplit
metadata: { name: api-split }
spec:
  service: api
  backends:
    - { service: api-v1, weight: 90 }
    - { service: api-v2, weight: 10 }
```

### 관찰 (Linkerd viz)
```bash
linkerd viz dashboard
# 자동: success rate, RPS, p95/p99, mTLS 표시
```

### Istio observability
- Kiali: service graph.
- Jaeger: tracing.
- Grafana: metrics.

### Ambient mode (Istio sidecar 없는)
- ztunnel (per-node) + waypoint proxy.
- 자원 효율 더 좋음.
- 새 (2024+).

### Trade-offs
```
장점:
- 코드 변경 X
- 통일 정책 (mTLS, retry, CB)
- Observability 자동

단점:
- 자원 (각 pod + sidecar)
- 복잡도 (특히 Istio)
- Latency (~1-3ms per hop)
- Debug 어려움
```

## 🤔 의사결정 기준
| 규모 | 추천 |
|---|---|
| <10 service | mesh 불필요 — 직접 |
| 10-100 service | Linkerd (가볍고 단순) |
| 큰 / 복잡 정책 | Istio |
| 자원 절약 | Linkerd 또는 Istio Ambient |
| GKE | Istio (기본 통합) |
| 자체 호스트 작은 팀 | Linkerd |

## ❌ 안티패턴
- **Mesh 도입 + 단순 정책**: overkill. ingress + library 충분.
- **모든 retry 같은 정책**: 어떤 endpoint 는 idempotent X.
- **CB 없이 cascading failure**: 한 service 죽으면 모두.
- **mTLS 가정 + 외부 통신**: gateway 만 mTLS — 외부 API 는 공개.
- **Sidecar resource 안 잡음**: pod scheduling 깨짐.
- **Istio 1.0 부터 풀 기능 도입**: 점진. STRICT mTLS 부터.
- **Egress 무제어**: 외부 호출 무제한.

## 🤖 LLM 활용 힌트
- Linkerd 시작 → 단순.
- Istio = 풀 기능, 학습 곡선.
- mTLS / retry / CB / observability 가 ROI 높음.

## 🔗 관련 문서
- [[Security_mTLS_Patterns]]
- [[DevOps_Kubernetes_Basics]]
- [[Backend_Circuit_Breaker]]
