4.3.4　创建流量镜像的Istio策略

默认情况下，Kubernetes在服务的两个版本之间进行负载均衡。创建如下流量镜像规则（具体代码参见sample-mirror-policy.yaml）将100%的流量发送到v1，同时指定流量镜像到v2。当流量被镜像时，请求将通过其主机/授权报头发送到镜像服务附上-shadow：

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: mirrorservice-sample
spec:
  host: mirrorservice-sample
  subsets:
  - name: v1
    labels:
      version: v1
  - name: v2
    labels:
      version: v2
---      
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: mirrorservice-sample
spec:
  hosts:
    - mirrorservice-sample
  http:
  - route:
    - destination:
        host: mirrorservice-sample
        subset: v1
      weight: 100
    mirror:
      host: mirrorservice-sample
      subset: v2