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ServiceEntry ​

ServiceEntry は、外部サービスを Istio service mesh に登録し、内部サービスと同様に管理できるようにします。

目次 ​

  1. ServiceEntry が必要な理由
  2. ServiceEntry の概要
  3. 名前解決モード
  4. ロケーション設定
  5. 実践例
  6. Egress Gateway との組み合わせ
  7. セキュリティと TLS
  8. モニタリングと制御
  9. ベストプラクティス

ServiceEntry が必要な理由 ​

外部サービス管理の必要性 ​

デフォルトでは、Istio mesh は外部サービスへのトラフィックを制御しません。ServiceEntry を使用すると、次のことが可能になります。

主な利点 ​

機能ServiceEntry なしServiceEntry あり
モニタリングブラックホール完全なメトリクス収集
トラフィック制御不可能Timeout、Retry、Circuit Breaker
セキュリティ限定的mTLS、証明書管理
Egress 制御すべての外部トラフィックを許可明示的な許可/ブロック
Service Discovery手動管理自動 DNS ルックアップ

ServiceEntry の概要 ​

ServiceEntry は、外部サービスを Istio service registry に追加します。

基本構造 ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-api
spec:
  hosts:                  # External service hostname
  - api.example.com
  ports:                  # Port and protocol
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL # External/internal location
  resolution: DNS         # Address resolution method

名前解決モード ​

ServiceEntry は 4 つのアドレス名前解決モードをサポートします。

1. DNS 名前解決 ​

最も一般的なモードで、DNS を介して IP アドレスを動的に名前解決します。

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-api-dns
spec:
  hosts:
  - api.example.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS  # DNS lookup

ユースケース:

  • パブリック API（AWS S3、Google Cloud Storage）
  • SaaS サービス（Stripe、SendGrid）
  • クラウドマネージドサービス

2. STATIC 名前解決 ​

固定 IP アドレスを明示的に指定します。

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-api-static
spec:
  hosts:
  - legacy-api.company.internal
  addresses:
  - 10.10.10.10
  - 10.10.10.11
  ports:
  - number: 8080
    name: http
    protocol: HTTP
  location: MESH_EXTERNAL
  resolution: STATIC  # Fixed IP
  endpoints:
  - address: 10.10.10.10
  - address: 10.10.10.11

ユースケース:

  • レガシーシステム（DNS なし）
  • 固定 IP を必要とするコンプライアンス要件
  • 内部データセンターサービス

3. NONE 名前解決 ​

アドレスの名前解決を実行せず、クライアントから提供されたアドレスをそのまま使用します。

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: wildcard-api
spec:
  hosts:
  - "*.api.example.com"  # Wildcard
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: NONE  # No address resolution

ユースケース:

  • ワイルドカードドメイン
  • クライアント側ロードバランシング
  • TCP/TLS proxy

4. DNS_ROUND_ROBIN 名前解決（非推奨） ​

DNS round robin を使用します（現在は DNS モードに統合されています）。

ロケーション設定 ​

MESH_EXTERNAL（外部サービス） ​

mesh 外部のサービスを登録します。

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-service
spec:
  hosts:
  - external-api.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL  # External service
  resolution: DNS

特性:

  • mTLS は適用されない
  • Egress Gateway 経由で送信可能
  • 外部トラフィックとして分類される

MESH_INTERNAL（内部サービス） ​

mesh 内部サービスとして扱います（使用されることはまれです）。

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: internal-vm-service
spec:
  hosts:
  - vm-service.internal
  ports:
  - number: 8080
    name: http
    protocol: HTTP
  location: MESH_INTERNAL  # Treat as internal service
  resolution: STATIC
  endpoints:
  - address: 10.0.0.5
    labels:
      app: vm-service

ユースケース:

  • VM workload を mesh に含める
  • マルチクラスター環境
  • ハイブリッドクラウド構成

実践例 ​

1. 外部 REST API の登録 ​

シナリオ: Payment Gateway API ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: payment-gateway-api
  namespace: production
spec:
  hosts:
  - api.payment-gateway.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
# VirtualService: Timeout and Retry settings
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: payment-gateway-routing
  namespace: production
spec:
  hosts:
  - api.payment-gateway.com
  http:
  - route:
    - destination:
        host: api.payment-gateway.com
    timeout: 10s
    retries:
      attempts: 3
      perTryTimeout: 3s
      retryOn: 5xx,reset,connect-failure
---
# DestinationRule: Circuit Breaker
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: payment-gateway-circuit-breaker
  namespace: production
spec:
  host: api.payment-gateway.com
  trafficPolicy:
    connectionPool:
      http:
        http1MaxPendingRequests: 10
        maxRequestsPerConnection: 1
    outlierDetection:
      consecutiveErrors: 3
      interval: 30s
      baseEjectionTime: 120s
    tls:
      mode: SIMPLE  # TLS connection

2. 外部データベースの登録 ​

シナリオ: AWS RDS MySQL ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: aws-rds-mysql
spec:
  hosts:
  - mydb.abc123.us-west-2.rds.amazonaws.com
  ports:
  - number: 3306
    name: tcp
    protocol: TCP
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: aws-rds-mysql-circuit-breaker
spec:
  host: mydb.abc123.us-west-2.rds.amazonaws.com
  trafficPolicy:
    connectionPool:
      tcp:
        maxConnections: 100
        connectTimeout: 5s
    outlierDetection:
      consecutiveErrors: 5
      interval: 60s
      baseEjectionTime: 60s

3. ワイルドカードドメインの登録 ​

シナリオ: AWS S3 Bucket へのアクセス ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: aws-s3-buckets
spec:
  hosts:
  - "*.s3.amazonaws.com"
  - "*.s3.*.amazonaws.com"
  - "*.s3-*.amazonaws.com"
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: NONE  # Use NONE for wildcards

4. 複数 Endpoint を持つ外部サービス ​

シナリオ: マルチリージョン API ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: multi-region-api
spec:
  hosts:
  - api.global-service.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: multi-region-routing
spec:
  hosts:
  - api.global-service.com
  http:
  # Region-based routing
  - match:
    - headers:
        x-region:
          exact: "us-west"
    route:
    - destination:
        host: api.global-service.com
      headers:
        request:
          set:
            Host: us-west.api.global-service.com

  - match:
    - headers:
        x-region:
          exact: "eu-central"
    route:
    - destination:
        host: api.global-service.com
      headers:
        request:
          set:
            Host: eu-central.api.global-service.com

  # Default routing
  - route:
    - destination:
        host: api.global-service.com

5. TCP Service の登録 ​

シナリオ: 外部 Redis Cluster ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-redis
spec:
  hosts:
  - redis.external-cluster.com
  addresses:
  - 203.0.113.10
  - 203.0.113.11
  ports:
  - number: 6379
    name: tcp
    protocol: TCP
  location: MESH_EXTERNAL
  resolution: STATIC
  endpoints:
  - address: 203.0.113.10
    labels:
      instance: primary
  - address: 203.0.113.11
    labels:
      instance: replica
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: external-redis-lb
spec:
  host: redis.external-cluster.com
  trafficPolicy:
    loadBalancer:
      simple: ROUND_ROBIN
    connectionPool:
      tcp:
        maxConnections: 50
        connectTimeout: 3s

Egress Gateway との組み合わせ ​

Egress Gateway を通じて外部トラフィックを一元的に制御します。

基本的な Egress Gateway 設定 ​

yaml
# ServiceEntry: Register external service
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-api
spec:
  hosts:
  - api.example.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
# Gateway: Egress Gateway configuration
apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
  name: egress-gateway
spec:
  selector:
    istio: egressgateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    hosts:
    - api.example.com
    tls:
      mode: PASSTHROUGH
---
# VirtualService: Mesh internal -> Egress Gateway
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: direct-api-through-egress
spec:
  hosts:
  - api.example.com
  gateways:
  - mesh
  - egress-gateway
  http:
  - match:
    - gateways:
      - mesh
      port: 443
    route:
    - destination:
        host: istio-egressgateway.istio-system.svc.cluster.local
        port:
          number: 443
  - match:
    - gateways:
      - egress-gateway
      port: 443
    route:
    - destination:
        host: api.example.com
        port:
          number: 443

TLS Origination（内部は HTTP、外部は HTTPS） ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-http-to-https
spec:
  hosts:
  - api.secure-service.com
  ports:
  - number: 80
    name: http
    protocol: HTTP
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: originate-tls
spec:
  host: api.secure-service.com
  trafficPolicy:
    portLevelSettings:
    - port:
        number: 80
      tls:
        mode: SIMPLE  # HTTP -> HTTPS conversion

セキュリティと TLS ​

外部サービスへの mTLS ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: mtls-external-service
spec:
  hosts:
  - mtls-api.example.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: mtls-external-tls
spec:
  host: mtls-api.example.com
  trafficPolicy:
    tls:
      mode: MUTUAL
      clientCertificate: /etc/certs/client-cert.pem
      privateKey: /etc/certs/client-key.pem
      caCertificates: /etc/certs/ca-cert.pem

SNI ルーティング ​

yaml
apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
  name: egress-sni-gateway
spec:
  selector:
    istio: egressgateway
  servers:
  - port:
      number: 443
      name: tls
      protocol: TLS
    hosts:
    - api.example.com
    - api2.example.com
    tls:
      mode: PASSTHROUGH
---
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: sni-routing
spec:
  hosts:
  - api.example.com
  - api2.example.com
  gateways:
  - mesh
  - egress-sni-gateway
  tls:
  - match:
    - gateways:
      - mesh
      port: 443
      sniHosts:
      - api.example.com
    route:
    - destination:
        host: istio-egressgateway.istio-system.svc.cluster.local
        port:
          number: 443
  - match:
    - gateways:
      - egress-sni-gateway
      port: 443
      sniHosts:
      - api.example.com
    route:
    - destination:
        host: api.example.com
        port:
          number: 443

モニタリングと制御 ​

メトリクス収集 ​

bash
# Check ServiceEntry traffic
kubectl exec -it <pod-name> -c istio-proxy -- \
  curl localhost:15000/stats/prometheus | grep "api.example.com"

# Egress traffic metrics
istio_requests_total{destination_service_name="api.example.com"}

Prometheus クエリ ​

yaml
# External service request count
sum(rate(istio_requests_total{destination_service_namespace="",destination_service_name="api.example.com"}[5m]))

# External service error rate
sum(rate(istio_requests_total{destination_service_name="api.example.com",response_code=~"5.."}[5m])) /
sum(rate(istio_requests_total{destination_service_name="api.example.com"}[5m]))

# External service response time
histogram_quantile(0.95,
  sum(rate(istio_request_duration_milliseconds_bucket{destination_service_name="api.example.com"}[5m])) by (le)
)

Egress トラフィックのブロック ​

yaml
# Block all Egress by default
apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: default
  namespace: default
spec:
  egress:
  - hosts:
    - "./*"  # Allow only same namespace
    - "istio-system/*"  # Allow istio-system
  outboundTrafficPolicy:
    mode: REGISTRY_ONLY  # Allow only those registered in ServiceEntry

ベストプラクティス ​

1. 明示的な ServiceEntry 登録 ​

yaml
# Good example: Explicit registration
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: payment-api
  namespace: production
  annotations:
    description: "Payment gateway API"
    owner: "payments-team"
    sla: "99.9%"
spec:
  hosts:
  - api.payment.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS

2. 常に Circuit Breaker を適用する ​

yaml
# Always apply Circuit Breaker for external services
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: external-api-protection
spec:
  host: api.example.com
  trafficPolicy:
    connectionPool:
      http:
        http1MaxPendingRequests: 10
        maxRequestsPerConnection: 1
    outlierDetection:
      consecutiveErrors: 3
      interval: 30s
      baseEjectionTime: 120s

3. Timeout 設定 ​

yaml
# Set explicit Timeout for external services
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: external-api-timeout
spec:
  hosts:
  - api.example.com
  http:
  - route:
    - destination:
        host: api.example.com
    timeout: 10s  # Explicit Timeout
    retries:
      attempts: 2
      perTryTimeout: 5s

4. Egress Gateway を使用する（本番環境） ​

yaml
# Control external traffic through Egress Gateway in production
# - Centralized monitoring
# - Easy IP whitelist management
# - Consistent security policies

5. Namespace 分離 ​

yaml
# Isolate ServiceEntry by namespace
apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: default
  namespace: team-a
spec:
  egress:
  - hosts:
    - "team-a/*"  # Only own namespace
    - "istio-system/*"
    - "external/*"  # Shared external services
  outboundTrafficPolicy:
    mode: REGISTRY_ONLY

6. ドキュメントテンプレート ​

yaml
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-service
  annotations:
    # Service information
    service-description: "Third-party payment API"
    service-owner: "payments-team@company.com"
    service-documentation: "https://wiki.company.com/payment-api"

    # SLA information
    sla-availability: "99.9%"
    sla-latency-p95: "500ms"
    rate-limit: "1000 req/min"

    # Cost information
    cost-per-request: "$0.01"
    monthly-budget: "$10000"

    # Incident response
    oncall: "payments-oncall"
    escalation: "CTO"
    fallback-strategy: "Use cached data"

参考資料 ​