> For the complete documentation index, see [llms.txt](https://atomoh.gitbook.io/kubernetes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://atomoh.gitbook.io/kubernetes/service-mesh/istio/traffic-management/10-session-affinity.md).

# Session Affinity

Session Affinity(또는 Sticky Session)는 동일한 사용자의 요청을 같은 파드로 라우팅하는 기법입니다.

## 목차

1. [Session Affinity 개요](#session-affinity-개요)
2. [Consistent Hash 기반](#consistent-hash-기반)
3. [Cookie 기반](#cookie-기반)
4. [Header 기반](#header-기반)
5. [실전 예제](#실전-예제)

## Session Affinity 개요

```mermaid
flowchart TB
    User[사용자 A]
    
    subgraph LB["Load Balancer"]
        Hash[Consistent Hash<br/>User ID 기반]
    end
    
    subgraph Pods["파드"]
        Pod1[Pod 1<br/>세션 A]
        Pod2[Pod 2]
        Pod3[Pod 3]
    end
    
    User -->|user_id=123| Hash
    Hash -->|항상 동일| Pod1
    
    %% 스타일 정의
    classDef user fill:#f9f9f9,stroke:#333,stroke-width:1px,color:black;
    classDef lb fill:#326CE5,stroke:#333,stroke-width:1px,color:white;
    classDef pod fill:#00C7B7,stroke:#333,stroke-width:1px,color:white;
    
    %% 클래스 적용
    class User user;
    class Hash lb;
    class Pod1,Pod2,Pod3 pod;
```

## Consistent Hash 기반

### HTTP Header 기반

```yaml
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-session-affinity
spec:
  host: reviews
  trafficPolicy:
    loadBalancer:
      consistentHash:
        httpHeaderName: "x-user-id"
```

### Cookie 기반

```yaml
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-cookie-affinity
spec:
  host: reviews
  trafficPolicy:
    loadBalancer:
      consistentHash:
        httpCookie:
          name: "session-id"
          ttl: 0s  # 쿠키 만료 시간 (0s = 세션 쿠키)
```

### Source IP 기반

```yaml
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-ip-affinity
spec:
  host: reviews
  trafficPolicy:
    loadBalancer:
      consistentHash:
        useSourceIp: true
```

## 참고 자료

* [Istio Session Affinity](https://istio.io/latest/docs/reference/config/networking/destination-rule/#LoadBalancerSettings-ConsistentHashLB)