服務發現

在Istio的Control Palne中，Pilot負責服務發現的相關工作。在Kubernetes 環境中，當有服務在Kubernetes 叢集中部屬時，Kubernetes 的服務註冊機制會記錄該服務的相關訊息。此時，Pilot會從Kubernetest API Server獲取這些訊息，並將這些資訊分發至各個Envoy代理中，且每個Envoy代理會更新配置已加入新部屬的服務訊息。

負載平衡

負載平衡是一種流量分配的機制，好的負載平衡策略可以提升效能，使用狀態適合的服務處理對應的流量，istio有提供基本的負載平衡策略，可以分別嘗試不同策略的效果，並選擇合適自己的策略。

這邊提供一個範例服務helloworld-v1與helloworld-v2

• Deployment

apiVersion: v1
kind: Service
metadata:
  name: helloworld-service
spec:
  type: ClusterIP
  selector:
    app: helloworld
  ports:
    - protocol: TCP
      name: http
      port: 5000
      targetPort: 5000
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: helloworld-v1
  labels:
    app: helloworld
spec:
  replicas: 1
  selector:
    matchLabels:
      app: helloworld
      version: v1
  template:
    metadata:
      labels:
        app: helloworld
        version: v1
    spec:
      containers:
      - name: helloworld-v1
        image: allenku0/hello-api:v1
        ports:
        - containerPort: 5000
        resources:
          limits:
            cpu: 500m
          requests:
            cpu: 200m

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: helloworld-v2
  labels:
    app: helloworld
spec:
  replicas: 1
  selector:
    matchLabels:
      app: helloworld
      version: v2
  template:
    metadata:
      labels:
        app: helloworld
        version: v2
    spec:
      containers:
      - name: helloworld-v2
        image: allenku0/hello-api:v2
        ports:
        - containerPort: 5000
        resources:
          limits:
            cpu: 500m
          requests:
            cpu: 200m

• VirtualService
  VirtualService:用於定義流量路由的規則，控制進入 Service Mesh 中的流量路由

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: hello-vs
spec:
  hosts:
  - "*"
  gateways:
  - hello-gateway
  http:
  - match:
    - uri:
        prefix: /api
    route:
    - destination:
        host: helloworld-service
        port:
          number: 5000
      

• DestinationRule
  DestinationRule 負責定義服務的策略，如負載平衡、Connection Pool與融斷等。

1. Round Robin

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: example-destination
spec:
  host: example-service
  trafficPolicy:
    loadBalancer:
      simple: ROUND_ROBIN

2. Random

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: example-destination
spec:
  host: example-service
  trafficPolicy:
    loadBalancer:
      simple: RANDOM

3. Least Request

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: example-destination
spec:
  host: example-service
  trafficPolicy:
    loadBalancer:
      simple: LEAST_CONN