Istio学习之CRD2⃣️：DestinationRule

今天来学习Istio关于流量管理的另一个CRD——DestinationRule，根据字面意思即目标规则，我们可以理解VirtualService为流量的路由，那么DestinationRule则为流量路由之后的去处。

介绍

首先献上官方文档：https://istio.io/latest/zh/docs/reference/config/networking/destination-rule/

样例

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: bookinfo-ratings
spec:
    # 含义同VirtualService中destination的host字段一致。
  host: ratings.prod.svc.cluster.local
  # 流量策略，包括负载均衡、连接池策略、异常点检查等
  trafficPolicy:
      # 负载均衡策略，支持随机负载均衡 /按权重负载均衡 /最少请求负载均衡 / hash轮训等
    loadBalancer:
      simple: LEAST_CONN
    # 连接池策略
    connectionPool:
        # tcp连接池设置
      tcp:
        maxConnections: 100
        connectTimeout: 30ms
        tcpKeepalive:
          time: 7200s
          interval: 75s
      http:
        http2MaxRequests: 1000
        maxRequestsPerConnection: 10
    # 异常点检查
    outlierDetection:
      consecutiveErrors: 7
      interval: 5m
      baseEjectionTime: 15m
    # tls设置
    tls:
      mode: MUTUAL
      clientCertificate: /etc/certs/myclientcert.pem
      privateKey: /etc/certs/client_private_key.pem
      caCertificates: /etc/certs/rootcacerts.pem
  # 服务端点集合
  subsets:
  # subset名称可以用于路由规则中的流量拆分，与virtualService的subset的引用
  - name: testversion
      # 使用标签对服务注册表中的服务端点进行筛选
    labels:
      version: v3
    trafficPolicy:
      loadBalancer:
        simple: ROUND_ROBIN

作用：我们可以通过结合virtualService，使用 Destination Rule 对流量划分不同的子集，根据不同的条件比如用户不同的身份、地址位置等条件的识别后的进行不同的流量路由，或者在版本更新的时候，使用灰度发布。
VirtualService对象和DestinationRule对象既可以单独使用、也可以结合使用。功能上VirtualService的功能之一是在后端不同Service中选择一个转发请求，而Service是在后端不同Pod中选择一个转发请求。DestinationRule是对不同后端的同一个Service上进行划分不同的subset。VirtualService和DestinationRule是通过subnet关联起来的。

演示

还是以上次VirtualService的httpd和tomcat例子为演示，首先创建对应的Deployment

httpd

apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpd
  labels:
    server: httpd
    app: web
spec:
  replicas: 1
  selector:
    matchLabels:
      server: httpd
      app: web
  template:
    metadata:
      labels:
        server: httpd
        app: web
    spec:
      containers:
      - name: busybox
        image: busybox
        imagePullPolicy: IfNotPresent
        command: ["/bin/sh", "-c", "echo 'this is httpd' > /var/www/index.html; httpd -f -p 8080 -h /var/www"]

tomcat

apiVersion: apps/v1
kind: Deployment
metadata:
  name: tomcat
  labels:
    server: tomcat
    app: web
spec:
  replicas: 1
  selector:
    matchLabels:
      server: tomcat
      app: web
  template:
    metadata:
      labels:
        server: tomcat
        app: web
    spec:
      containers:
      - name: tomcat
        image: docker.io/kubeguide/tomcat-app:v1
        imagePullPolicy: IfNotPresent

创建对应的service

apiVersion: v1
kind: Service
metadata:
  name: web-svc
spec:
  selector:
    app: web
  ports:
  - name: http
    port: 8080
    targetPort: 8080
    protocol: TCP

使用DestinationRule根据label将我们的流量划分为不同的版本，假设把httpd为我们服务的v1版本，tomcat为v2版本，使用VirtualService进行不同的路由

```yaml apiVersion: networking.istio.io/v1alpha3 kind: DestinationRule metadata: name: demo-des spec: host: web-svc subsets:
- name: v1 labels: server: httpd
- name: v2 labels: server: tomcat

apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: web-svc-vs3 spec: hosts:

- web-svc
http:
- route:
  - destination:
      host: web-svc
      subset: v2


+ 创建busybox进入测试

  ```yaml
  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: hexiaohong-client
  spec:
    replicas: 1
    selector:
      matchLabels:
        app: hexiaohong-client
    template:
      metadata:
        labels:
          app: hexiaohong-client
      spec:
        containers:
        - name: busybox
          image: busybox
          imagePullPolicy: IfNotPresent
          command: ["/bin/sh", "-c", "sleep 3600"]

  ---
  apiVersion: v1
  kind: Service
  metadata:
    name: hexiaohong-client-svc
  spec:
    selector:
      app: hexiaohong-client
    ports:
    - name: http
      port: 8080
      targetPort: 8080
      protocol: TCP

查看virtualService与DestinationRule
进入busybox 请求
使用kubectl edit virtualservices XXX，修改subset的版本为v2，进入busybox请求，流量则导入到v2/tomcat去了

DestinationRule

Istio学习之CRD2⃣️：DestinationRule

介绍

演示

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