云原生系统之弹性模式

services.AddHttpClient("small")
        //降级
        .AddPolicyHandler(Policy<HttpResponseMessage>.HandleInner<Exception>().FallbackAsync(new HttpResponseMessage(),async b =>
        {
           // 1、降级打印异常
          Console.WriteLine($"服务开始降级,上游异常消息：{b.Exception.Message}");
          // 2、降级后的数据
          b.Result.Content= new StringContent("请求太多，请稍后重试", Encoding.UTF8, "text/html");
          b.Result.StatusCode = HttpStatusCode.TooManyRequests;
          await Task.CompletedTask;
        }))
        //熔断                                                      
        .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<Exception>() 
           .CircuitBreakerAsync(
              3,    // 打开断路器之前失败的次数
              TimeSpan.FromSeconds(20), // 断路器的开启的时间间隔
              (ex, ts) =>  //熔断器开启
              {
                  Console.WriteLine($"服务断路器开启，异常消息：{ex.Exception.Message}");
                  Console.WriteLine($"服务断路器开启的时间：{ts.TotalSeconds}s");
              }, 
              () => { Console.WriteLine($"服务断路器重置"); },   //断路器重置事件
              () => { Console.WriteLine($"服务断路器半开启(一会开，一会关)"); }  //断路器半开启事件
            )
        )
        //重试
        .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<Exception>().RetryAsync(3))
       // 超时 
       .AddPolicyHandler(Policy.TimeoutAsync<HttpResponseMessage>(TimeSpan.FromSeconds(2))); 
       

type Settings struct {
    Name          string
    MaxRequests   uint32       #半开状态允许的最大请求数量，默认为0，允许1个请求
    Interval      time.Duration
    Timeout       time.Duration  # 断路器进入半开状态的间隔，默认60s
    ReadyToTrip   func(counts Counts) bool   # 切换状态的逻辑
    OnStateChange func(name string, from State, to State)
}

package main
import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "github.com/sony/gobreaker"
)
var cb *gobreaker.CircuitBreaker
func init() {
    var st gobreaker.Settings
    st.Name = "HTTP GET"
    st.ReadyToTrip = func(counts gobreaker.Counts) bool {
        failureRatio := float64(counts.TotalFailures) / float64(counts.Requests)
        return counts.Requests >= 3 && failureRatio >= 0.6
    }
    cb = gobreaker.NewCircuitBreaker(st)
}
// Get wraps http.Get in CircuitBreaker.
func Get(url string) ([]byte, error) {
    body, err := cb.Execute(func() (interface{}, error) {
        resp, err := http.Get(url)
        if err != nil {
            return nil, err
        }
        defer resp.Body.Close()
        body, err := ioutil.ReadAll(resp.Body)
        if err != nil {
            return nil, err
        }
        return body, nil
    })
    if err != nil {
        return nil, err
    }
    return body.([]byte), nil
}
func main() {
    body, err := Get("http://www.google.com/robots.txt")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(body))
}