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)
}
query2019/05/09 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
query 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
query 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。