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 mainimport (    "fmt"    "io/ioutil"    "log"    "net/http"    "github.com/sony/gobreaker")var cb *gobreaker.CircuitBreakerfunc 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))}