golang的熔断包hystrix的用例

服务器的熔断机制是个大话题，可以参考这篇文章一窥究竟： 熔断，限流，降级
。

Netflix的熔断系统Hystrix很有效，并提供了golang的包： https://github.com/afex/hystrix-go
。来看看参数如何使用，代码中的默认配置定义为：

var (
    // DefaultTimeout is how long to wait for command to complete, in milliseconds
    DefaultTimeout = 1000
    // DefaultMaxConcurrent is how many commands of the same type can run at the same time
    DefaultMaxConcurrent = 10
    // DefaultVolumeThreshold is the minimum number of requests needed before a circuit can be tripped due to health
    DefaultVolumeThreshold = 20
    // DefaultSleepWindow is how long, in milliseconds, to wait after a circuit opens before testing for recovery
    DefaultSleepWindow = 5000
    // DefaultErrorPercentThreshold causes circuits to open once the rolling measure of errors exceeds this percent of requests
    DefaultErrorPercentThreshold = 50
)

RequestVolumeThreshold 指明某个command在多少次调用之后开始探测熔断

package main

import (
    "errors"
    "log"
    "math/rand"
    "third/hystrix"
    "time"
)

func init() {
    hystrix.ConfigureCommand("seckill", hystrix.CommandConfig{
        Timeout:                1, //cmd的超时时间，一旦超时则返回失败
        MaxConcurrentRequests:  1, //最大并发请求数
        RequestVolumeThreshold: 1, //熔断探测前的调用次数
        SleepWindow:            1000, //熔断发生后的等待恢复时间
        ErrorPercentThreshold:  10,//失败占比
    })
}

var Gcount, Gerror int

func testHystrix() error {

    query := func() error {
        var err error
        r := rand.Float64()
        Gcount++
        if r < 1 {
            err = errors.New("bad luck")
            Gerror++
            return err
        } else {
            time.Sleep(20 * time.Millisecond)
        }

        return nil
    }

    service := "seckill"
    var err error
    err = hystrix.Do(service, func() error {
        err = query()
        return err
    }, nil)

    return err
}

func main() {
    for i := 0; i < 10; i++ {
        err := testHystrix()
        if err != nil {
            log.Printf("testHystrix error:%v", err)
        }
    }

    log.Printf("Gcount:%d Gerror:%d", Gcount, Gerror)
}

如上，RequestVolumeThreshold 为1，则第二次调用开始探测，由于所有调用全部失败，则熔断立马被触发，后续调用全部不能触达 query
函数。

2019/05/09 15:15:15 testHystrix error:bad luck
2019/05/09 15:15:15 hystrix-go: opening circuit seckill
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 15:15:15 testHystrix error:hystrix: circuit open
2019/05/09 16:02:56 Gcount:1 Gerror:1

Process finished with exit code 0

最后的结果为调用了一次，失败一次。

SleepWindow 指明在熔断发生后何时开始探测其是否恢复，单位毫秒

修改参数为：

   hystrix.ConfigureCommand("seckill", hystrix.CommandConfig{
        Timeout:                1, //cmd的超时时间，一旦超时则返回失败
        MaxConcurrentRequests:  1, //最大并发请求数
        RequestVolumeThreshold: 1, //熔断探测前的调用次数
        SleepWindow:            1, //熔断发生后的等待恢复时间
        ErrorPercentThreshold:  10,//失败占比
    })

熔断发生后1毫秒后就开始探测是否恢复，当然结果还是继续失败：

2019/05/09 16:36:21 testHystrix error:bad luck
2019/05/09 16:36:21 hystrix-go: opening circuit seckill
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 testHystrix error:hystrix: circuit open
2019/05/09 16:36:21 hystrix-go: allowing single test to possibly close circuit seckill
2019/05/09 16:36:21 testHystrix error:hystrix: timeout
2019/05/09 16:36:21 Gcount:2 Gerror:2

Process finished with exit code 0

最后的结果为调用了两次，失败两次。

Timeout 指明command的执行超时时间，单位毫秒

参数为原始参数。修改 query
函数：

   query := func() error {
        var err error
        r := rand.Float64()
        Gcount++
        if r < 0 {
            err = errors.New("bad luck")
            Gerror++
            return err
        } else {
            time.Sleep(20 * time.Millisecond)
        }

        return nil
    }

所有调用都超时，结果为调用了一次，失败0次。

2019/05/09 16:49:43 testHystrix error:hystrix: timeout
2019/05/09 16:49:43 hystrix-go: opening circuit seckill
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 testHystrix error:hystrix: circuit open
2019/05/09 16:49:43 Gcount:1 Gerror:0

Process finished with exit code 0

ErrorPercentThreshold 指明熔断的触发条件：失败调用占总调用次数的比例

参数为原始参数。修改 query
函数：

   query := func() error {
        var err error
        r := rand.Float64()
        Gcount++
        if r < 0.1 {
            err = errors.New("bad luck")
            Gerror++
            return err
        } else {
            time.Sleep(20 * time.Millisecond)
        }

        return nil
    }

测试100次，结果太长不贴了，核心就是失败次数占总次数的比例，触发熔断之后清空，待恢复之后重新计算。

MaxConcurrentRequests 指明最大并发数，很好理解了