Istio超时与重试

一、理解超时与重试
　　超时的原理是，如果程序请求长时间无法返回结果，则需要设置超时机制，超过设置的时间则返回错误的信息；这样做既可以节约等待时消耗的资源，也可以避免由于级联错误引起的一系列问题。设置超时的方式也有很多种，比如通过修改代码在应用程序侧设置请求超时时间，但是这样非常的不灵活，也很容易出现遗漏的现象，而Istio则可以在基础设施层解决这一问题。
　　重试的原理是，在网络环境不稳定的情况下，会出现暂时的网络不可达的现象，这时就需要重试机制，通过多次的尝试来获取正确的返回信息。
　　

二、配置超时

1）设置默认的目标规则

在目标规则中定义可用的版本

➜  kubectl apply -f ../../samples/bookinfo/networking/destination-rule-all.yaml 
destinationrule.networking.istio.io/productpage created
destinationrule.networking.istio.io/reviews created
destinationrule.networking.istio.io/ratings created
destinationrule.networking.istio.io/details created

2）初始化版本路由

➜  kubectl apply -f ../../samples/bookinfo/networking/virtual-service-all-v1.yaml 
virtualservice.networking.istio.io/productpage created
virtualservice.networking.istio.io/reviews created
virtualservice.networking.istio.io/ratings created
virtualservice.networking.istio.io/details created

3）设置虚拟服务
　　通过配置路由规则（HTTPRoute）的timeout字段来指定http请求的超时时间（默认情况下，超时是被禁用的）；配置reviews服务，将请求路由到v2的版本上，使其可以发起对ratings服务的调用。

➜  kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: reviews
spec:
  hosts:
    - reviews
  http:
  - route:
    - destination:
        host: reviews
        subset: v2
EOF
virtualservice.networking.istio.io/reviews configured

➜  kubectl describe vs reviews                    
Name:         reviews
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  networking.istio.io/v1beta1
Kind:         VirtualService
Metadata:
  Creation Timestamp:  2021-07-24T09:23:41Z
  Generation:          2
  Managed Fields:
    API Version:  networking.istio.io/v1alpha3
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .:
          f:kubectl.kubernetes.io/last-applied-configuration:
      f:spec:
        .:
        f:hosts:
        f:http:
    Manager:         kubectl-client-side-apply
    Operation:       Update
    Time:            2021-07-24T09:23:41Z
  Resource Version:  645195
  Self Link:         /apis/networking.istio.io/v1beta1/namespaces/default/virtualservices/reviews
  UID:               65fea820-0b25-4616-ae0e-c628bef8dc13
Spec:
  Hosts:
    reviews
  Http:
    Route:
      Destination:
        Host:    reviews
        Subset:  v2
Events:          <none>

4）给ratings服务的调用注入2秒延迟的故障

➜  kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: ratings
spec:
  hosts:
  - ratings
  http:
  - fault:
      delay:
        percent: 100
        fixedDelay: 2s
    route:
    - destination:
        host: ratings
        subset: v1
EOF
virtualservice.networking.istio.io/ratings configured

➜  kubectl describe vs ratings 
Name:         ratings
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  networking.istio.io/v1beta1
Kind:         VirtualService
Metadata:
  Creation Timestamp:  2021-07-24T09:23:42Z
  Generation:          2
  Managed Fields:
    API Version:  networking.istio.io/v1alpha3
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .:
          f:kubectl.kubernetes.io/last-applied-configuration:
      f:spec:
        .:
        f:hosts:
        f:http:
    Manager:         kubectl-client-side-apply
    Operation:       Update
    Time:            2021-07-24T09:23:42Z
  Resource Version:  645606
  Self Link:         /apis/networking.istio.io/v1beta1/namespaces/default/virtualservices/ratings
  UID:               5f2f821e-932c-40c2-95ae-c3ac6ef02dcf
Spec:
  Hosts:
    ratings
  Http:
    Fault:
      Delay:
        Fixed Delay:  2s
        Percent:      100
    Route:
      Destination:
        Host:    ratings
        Subset:  v1
Events:          <none>

5）请求服务查看延迟

➜  curl -o /dev/null -s -w "time_starttransfer:%{time_starttransfer}\ntime_total:%{time_total}\n" http://localhost/productpage
time_starttransfer:2.094652
time_total:2.094805

6）给reviews服务调用增加一个0.5秒的请求超时

➜  kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: reviews
spec:
  hosts:
  - reviews
  http:
  - route:
    - destination:
        host: reviews
        subset: v2
    timeout: 0.5s
EOF
virtualservice.networking.istio.io