云原生系統(tǒng)之彈性模式

services.AddHttpClient("small")        //降級        .AddPolicyHandler(Policy<HttpResponseMessage>.HandleInner<Exception>().FallbackAsync(new HttpResponseMessage(),async b =>        {           // 1、降級打印異常          Console.WriteLine($"服務(wù)開始降級,上游異常消息：{b.Exception.Message}");          // 2、降級后的數(shù)據(jù)          b.Result.Content= new StringContent("請求太多，請稍后重試", Encoding.UTF8, "text/html");          b.Result.StatusCode = HttpStatusCode.TooManyRequests;          await Task.CompletedTask;        }))        //熔斷                                                              .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<Exception>()            .CircuitBreakerAsync(              3,    // 打開斷路器之前失敗的次數(shù)              TimeSpan.FromSeconds(20), // 斷路器的開啟的時間間隔              (ex, ts) =>  //熔斷器開啟              {                  Console.WriteLine($"服務(wù)斷路器開啟，異常消息：{ex.Exception.Message}");                  Console.WriteLine($"服務(wù)斷路器開啟的時間：{ts.TotalSeconds}s");              },               () => { Console.WriteLine($"服務(wù)斷路器重置"); },   //斷路器重置事件              () => { Console.WriteLine($"服務(wù)斷路器半開啟(一會開，一會關(guān))"); }  //斷路器半開啟事件            )        )        //重試        .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<Exception>().RetryAsync(3))       // 超時        .AddPolicyHandler(Policy.TimeoutAsync<HttpResponseMessage>(TimeSpan.FromSeconds(2)));        

type Settings struct {    Name          string    MaxRequests   uint32       #半開狀態(tài)允許的最大請求數(shù)量，默認(rèn)為0，允許1個請求    Interval      time.Duration    Timeout       time.Duration  # 斷路器進(jìn)入半開狀態(tài)的間隔，默認(rèn)60s    ReadyToTrip   func(counts Counts) bool   # 切換狀態(tài)的邏輯    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))}