一、服务雪崩

服务雪崩原因
服务雪崩应对策略

在这里插入图片描述

二、熔断-限流-降级概述

限流和熔断最终都会导致用户的体验降级

限流：流量2k，但是我的服务能力只有1k，所以这个时候多出来的流量怎么办？
- a.拒绝；
- b.排队等待；
用户体验
- 用户体验不好：当前访问用户过多，请稍后重试
- 用户体验降级：原本是访问流畅，下单流畅 -> 当前访问用户过多，请稍后重试
熔断：
- 比如A服务访问B服务，这时候B服务很慢（B服务压力过大，导致了出现不少请求错误），调用方很容易出现一个问题：每次调用都超时
- 结果这个时候数据库出现了问题，超时重试，导致网络2k的流量突然变成了3k，这让原本满负荷的B服务雪上加霜，B服务宕机
- 如果这时候有一种熔断机制（比较恰当的比喻如保险丝）
  - a.发现了大部分请求很慢，50%请求都很慢
  - b.发现请求有50%都错误了
  - c.错误数量很多，比如1s出现了20个错误

三、熔断限流技术选型

Hystrix官网：https://github.com/Netflix/Hystrix；Netflix开源的，已经不维护了
Sentinel：https://github.com/alibaba/Sentinel；阿里开源的，一直在维护
sentinel-golang：https://github.com/alibaba/sentinel-golang

	Sentinel	Hystrix
隔离策略	信号量隔离	线程池隔离/信号量隔离
熔断降级策略	基于响应时间或失败比率	基于失败比率
实时指标实现	滑动窗口	滑动窗口（基于RxJava）
规则配置	支持多种数据源	支持多种数据源
扩展性	多个扩展点	插件的形式
基于注解的支持	支持	支持
限流	基于QPS，支持基于调用关系的限流	有限的支持
流量整形	支持慢启动、匀速器模式	不支持
系统负载保护	支持	不支持
控制台	开箱即用，可配置规则，查看秒级监控、机器发现等	不完善
常见框架的适配	Servlet、Spring Cloud、Dubbo、gRpc等	Servlet、Spring Cloud Netflix

四、sentinel限流

1 - 基于QPS限流

基于QPS限流：
- Entry表示入口，base.Inbound表示入流量
- StatIntervalInMs: 规则对应的流量控制器的独立统计结构的统计周期。如果StatIntervalInMs是1000，也就是统计QPS
- 测试结果是之前10次都是检查通过，第11次和第12次限流
ControlBehavior：表示表示流量控制器的控制行为，目前 Sentinel 支持两种控制行为
- Reject：表示如果当前统计周期内，统计结构统计的请求数超过了阈值，就直接拒绝
- Throttling：表示匀速排队的统计策略。它的中心思想是，以固定的间隔时间让请求通过
Throttling匀速排队
Reject策略

package main

import (
	"fmt"
	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/base"
	"github.com/alibaba/sentinel-golang/core/flow"
	"log"
)

func main() {
	//先初始化sentinel
	err := sentinel.InitDefault()
	if err != nil {
		log.Fatalf("初始化sentinel 异常: %v", err)
	}

	//配置限流规则
	_, err = flow.LoadRules([]*flow.Rule{
		{
			Resource:               "some-test",
			TokenCalculateStrategy: flow.Direct,
			ControlBehavior:        flow.Reject, //匀速通过
			Threshold:              10,
			StatIntervalInMs:       1000,
		},

		{
			Resource:               "some-test2",
			TokenCalculateStrategy: flow.Direct,
			ControlBehavior:        flow.Reject, //直接拒绝
			Threshold:              10,
			StatIntervalInMs:       1000,
		},
	})

	if err != nil {
		log.Fatalf("加载规则失败: %v", err)
	}

	for i := 0; i < 12; i++ {
		e, b := sentinel.Entry("some-test", sentinel.WithTrafficType(base.Inbound))
		if b != nil {
			fmt.Println("限流了")
		} else {
			fmt.Println("检查通过")
			e.Exit()
		}
	}
}

在这里插入图片描述

2 - Throttling策略

Throttling策略：修改 ControlBehavior: flow.Throttling, //匀速通过

package main

import (
	"fmt"
	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/base"
	"github.com/alibaba/sentinel-golang/core/flow"
	"log"
)

func main() {
	//先初始化sentinel
	err := sentinel.InitDefault()
	if err != nil {
		log.Fatalf("初始化sentinel 异常: %v", err)
	}

	//配置限流规则
	_, err = flow.LoadRules([]*flow.Rule{
		{
			Resource:               "some-test",
			TokenCalculateStrategy: flow.Direct,
			ControlBehavior:        flow.Throttling, //匀速通过
			Threshold:              10,
			StatIntervalInMs:       1000,
		},
	})

	if err != nil {
		log.Fatalf("加载规则失败: %v", err)
	}

	for i := 0; i < 12; i++ {
		e, b := sentinel.Entry("some-test", sentinel.WithTrafficType(base.Inbound))
		if b != nil {
			fmt.Println("限流了")
		} else {
			fmt.Println("检查通过")
			e.Exit()
		}
	}
}

在这里插入图片描述

验证Throttling策略：我们在每个Entry后添加sleep 101ms，结果就是全部通过

package main

import (
	"fmt"
	"log"
	"time"

	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/base"
	"github.com/alibaba/sentinel-golang/core/flow"
)

func main() {
	//先初始化sentinel
	err := sentinel.InitDefault()
	if err != nil {
		log.Fatalf("初始化sentinel 异常: %v", err)
	}

	//配置限流规则
	_, err = flow.LoadRules([]*flow.Rule{
		{
			Resource:               "some-test",
			TokenCalculateStrategy: flow.Direct,
			ControlBehavior:        flow.Throttling, //匀速通过
			Threshold:              10,
			StatIntervalInMs:       1000,
		},
	})

	if err != nil {
		log.Fatalf("加载规则失败: %v", err)
	}

	for i := 0; i < 12; i++ {
		e, b := sentinel.Entry("some-test", sentinel.WithTrafficType(base.Inbound))
		if b != nil {
			fmt.Println("限流了")
		} else {
			fmt.Println("检查通过")
			e.Exit()
		}
		time.Sleep(101 * time.Millisecond)
	}
}

在这里插入图片描述

3 - sentinel预热/冷启动

WarmUp：即预热/冷启动方式。当系统长期处于低水位的情况下，当流量突然增加时，直接把系统拉升到高水位可能瞬间把系统压垮。通过"冷启动"，让通过的流量缓慢增加，在一定时间内逐渐增加到阈值上限，给冷系统一个预热的时间，避免冷系统被压垮

在这里插入图片描述

测试预热

package main

import (
	"fmt"
	"log"
	"math/rand"
	"time"

	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/base"
	"github.com/alibaba/sentinel-golang/core/flow"
)

func main() {
	//先初始化sentinel
	err := sentinel.InitDefault()
	if err != nil {
		log.Fatalf("初始化sentinel 异常: %v", err)
	}

	var globalTotal int
	var passTotal int
	var blockTotal int
	ch := make(chan struct{})

	//配置限流规则
	_, err = flow.LoadRules([]*flow.Rule{
		{
			Resource:               "some-test",
			TokenCalculateStrategy: flow.WarmUp, //冷启动策略
			ControlBehavior:        flow.Reject, //直接拒绝
			Threshold:              1000,
			WarmUpPeriodSec:        30,
		},
	})

	if err != nil {
		log.Fatalf("加载规则失败: %v", err)
	}

	//我会在每一秒统计一次，这一秒只能 你通过了多少，总共有多少， block了多少, 每一秒会产生很多的block
	for i := 0; i < 100; i++ {
		go func() {
			for {
				globalTotal++
				e, b := sentinel.Entry("some-test", sentinel.WithTrafficType(base.Inbound))
				if b != nil {
					//fmt.Println("限流了")
					blockTotal++
					time.Sleep(time.Duration(rand.Uint64()%10) * time.Millisecond)
				} else {
					passTotal++
					time.Sleep(time.Duration(rand.Uint64()%10) * time.Millisecond)
					e.Exit()
				}
			}
		}()
	}

	go func() {
		var oldTotal int //过去1s总共有多少个
		var oldPass int  //过去1s总共pass多少个
		var oldBlock int //过去1s总共block多少个
		for {
			oneSecondTotal := globalTotal - oldTotal
			oldTotal = globalTotal

			oneSecondPass := passTotal - oldPass
			oldPass = passTotal

			oneSecondBlock := blockTotal - oldBlock
			oldBlock = blockTotal

			time.Sleep(time.Second)
			fmt.Printf("total:%d, pass:%d, block:%d\n", oneSecondTotal, oneSecondPass, oneSecondBlock)
		}
	}()

	<-ch
}

在这里插入图片描述

五、sentinel熔断

1 - 熔断器模型

sentinel熔断器模型：Sentinel 熔断降级基于熔断器模式 (circuit breaker pattern) 实现。熔断器内部维护了一个熔断器的状态机

在这里插入图片描述

熔断器有三种状态
- Closed 状态：也是初始状态，该状态下，熔断器会保持闭合，对资源的访问直接通过熔断器的检查
- Open 状态：断开状态，熔断器处于开启状态，对资源的访问会被切断
- Half-Open 状态：半开状态，该状态下除了探测流量，其余对资源的访问也会被切断。探测流量指熔断器处于半开状态时，会周期性的允许一定数目的探测请求通过，如果探测请求能够正常的返回，代表探测成功，此时熔断器会重置状态到 Closed 状态，结束熔断；如果探测失败，则回滚到 Open 状态
静默期：
- Sentinel 熔断器的三种熔断策略都支持静默期 (规则中通过MinRequestAmount字段表示)
- 静默期是指一个最小的静默请求数，在一个统计周期内，如果对资源的请求数小于设置的静默数，那么熔断器将不会基于其统计值去更改熔断器的状态
- 静默期的设计理由也很简单，举个例子，假设在一个统计周期刚刚开始时候，第 1 个请求碰巧是个慢请求，这个时候这个时候的慢调用比例就会是 100%，很明显是不合理，所以存在一定的巧合性
- 所以静默期提高了熔断器的精准性以及降低误判可能性

2 - 基于错误数熔断

package main

import (
	"errors"
	"fmt"
	"log"
	"math/rand"
	"time"

	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/circuitbreaker"
	"github.com/alibaba/sentinel-golang/core/config"
	"github.com/alibaba/sentinel-golang/logging"
	"github.com/alibaba/sentinel-golang/util"
)

type stateChangeTestListener struct {
}

func (s *stateChangeTestListener) OnTransformToClosed(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Closed, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToOpen(prev circuitbreaker.State, rule circuitbreaker.Rule, snapshot interface{}) {
	fmt.Printf("rule.steategy: %+v, From %s to Open, snapshot: %d, time: %d\n", rule.Strategy, prev.String(), snapshot, util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToHalfOpen(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Half-Open, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func main() {
	total := 0
	totalPass := 0
	totalBlock := 0
	totalErr := 0
	conf := config.NewDefaultConfig()
	// for testing, logging output to console
	conf.Sentinel.Log.Logger = logging.NewConsoleLogger()
	err := sentinel.InitWithConfig(conf)
	if err != nil {
		log.Fatal(err)
	}
	ch := make(chan struct{})
	// Register a state change listener so that we could observer the state change of the internal circuit breaker.
	circuitbreaker.RegisterStateChangeListeners(&stateChangeTestListener{})

	_, err = circuitbreaker.LoadRules([]*circuitbreaker.Rule{
		// Statistic time span=10s, recoveryTimeout=3s, maxErrorCount=50
		{
			Resource:         "abc",
			Strategy:         circuitbreaker.ErrorCount,
			RetryTimeoutMs:   3000, //3s之后尝试恢复
			MinRequestAmount: 10,   //静默数
			StatIntervalMs:   5000,
			Threshold:        50,
		},
	})
	if err != nil {
		log.Fatal(err)
	}

	logging.Info("[CircuitBreaker ErrorCount] Sentinel Go circuit breaking demo is running. You may see the pass/block metric in the metric log.")
	go func() {
		for {
			total++
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g1 blocked
				totalBlock++
				fmt.Println("协程熔断了")
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				totalPass++
				if rand.Uint64()%20 > 9 {
					totalErr++
					// Record current invocation as error.
					sentinel.TraceError(e, errors.New("biz error"))
				}
				// g1 passed
				time.Sleep(time.Duration(rand.Uint64()%20+10) * time.Millisecond)
				e.Exit()
			}
		}
	}()
	go func() {
		for {
			total++
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g2 blocked
				totalBlock++
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				// g2 passed
				totalPass++
				time.Sleep(time.Duration(rand.Uint64()%80) * time.Millisecond)
				e.Exit()
			}
		}
	}()

	go func() {
		for {
			time.Sleep(time.Second)
			fmt.Println(totalErr)
		}
	}()
	<-ch
}

在这里插入图片描述

3 - 基于错误率熔断

package main

import (
	"errors"
	"fmt"
	"log"
	"math/rand"
	"time"

	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/circuitbreaker"
	"github.com/alibaba/sentinel-golang/core/config"
	"github.com/alibaba/sentinel-golang/logging"
	"github.com/alibaba/sentinel-golang/util"
)

type stateChangeTestListener struct {
}

func (s *stateChangeTestListener) OnTransformToClosed(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Closed, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToOpen(prev circuitbreaker.State, rule circuitbreaker.Rule, snapshot interface{}) {
	fmt.Printf("rule.steategy: %+v, From %s to Open, snapshot: %.2f, time: %d\n", rule.Strategy, prev.String(), snapshot, util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToHalfOpen(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Half-Open, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func main() {
	total := 0
	totalPass := 0
	totalBlock := 0
	totalErr := 0
	conf := config.NewDefaultConfig()
	// for testing, logging output to console
	conf.Sentinel.Log.Logger = logging.NewConsoleLogger()
	err := sentinel.InitWithConfig(conf)
	if err != nil {
		log.Fatal(err)
	}
	ch := make(chan struct{})
	// Register a state change listener so that we could observer the state change of the internal circuit breaker.
	circuitbreaker.RegisterStateChangeListeners(&stateChangeTestListener{})

	_, err = circuitbreaker.LoadRules([]*circuitbreaker.Rule{
		// Statistic time span=10s, recoveryTimeout=3s, maxErrorCount=50
		{
			Resource:         "abc",
			Strategy:         circuitbreaker.ErrorRatio,
			RetryTimeoutMs:   3000, //3s之后尝试恢复
			MinRequestAmount: 10,   //静默数
			StatIntervalMs:   5000,
			Threshold:        0.4,
		},
	})
	if err != nil {
		log.Fatal(err)
	}

	logging.Info("[CircuitBreaker ErrorCount] Sentinel Go circuit breaking demo is running. You may see the pass/block metric in the metric log.")
	go func() {
		for {
			total++
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g1 blocked
				totalBlock++
				fmt.Println("协程熔断了")
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				totalPass++
				if rand.Uint64()%20 > 9 {
					totalErr++
					// Record current invocation as error.
					sentinel.TraceError(e, errors.New("biz error"))
				}
				// g1 passed
				time.Sleep(time.Duration(rand.Uint64()%40+10) * time.Millisecond)
				e.Exit()
			}
		}
	}()
	go func() {
		for {
			total++
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g2 blocked
				totalBlock++
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				// g2 passed
				totalPass++
				time.Sleep(time.Duration(rand.Uint64()%80) * time.Millisecond)
				e.Exit()
			}
		}
	}()

	go func() {
		for {
			time.Sleep(time.Second)
			fmt.Println(float64(totalErr) / float64(total))
		}
	}()
	<-ch
}

在这里插入图片描述

4 - 基于慢请求熔断

package main

import (
	"errors"
	"fmt"
	"log"
	"math/rand"
	"time"

	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/circuitbreaker"
	"github.com/alibaba/sentinel-golang/core/config"
	"github.com/alibaba/sentinel-golang/logging"
	"github.com/alibaba/sentinel-golang/util"
)

type stateChangeTestListener struct {
}

func (s *stateChangeTestListener) OnTransformToClosed(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Closed, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToOpen(prev circuitbreaker.State, rule circuitbreaker.Rule, snapshot interface{}) {
	fmt.Printf("rule.steategy: %+v, From %s to Open, snapshot: %.2f, time: %d\n", rule.Strategy, prev.String(), snapshot, util.CurrentTimeMillis())
}

func (s *stateChangeTestListener) OnTransformToHalfOpen(prev circuitbreaker.State, rule circuitbreaker.Rule) {
	fmt.Printf("rule.steategy: %+v, From %s to Half-Open, time: %d\n", rule.Strategy, prev.String(), util.CurrentTimeMillis())
}

func main() {
	conf := config.NewDefaultConfig()
	// for testing, logging output to console
	conf.Sentinel.Log.Logger = logging.NewConsoleLogger()
	err := sentinel.InitWithConfig(conf)
	if err != nil {
		log.Fatal(err)
	}
	ch := make(chan struct{})
	// Register a state change listener so that we could observer the state change of the internal circuit breaker.
	circuitbreaker.RegisterStateChangeListeners(&stateChangeTestListener{})

	_, err = circuitbreaker.LoadRules([]*circuitbreaker.Rule{
		// Statistic time span=10s, recoveryTimeout=3s, slowRtUpperBound=50ms, maxSlowRequestRatio=50%
		{
			Resource:         "abc",
			Strategy:         circuitbreaker.SlowRequestRatio,
			RetryTimeoutMs:   3000,
			MinRequestAmount: 10,
			StatIntervalMs:   5000,
			MaxAllowedRtMs:   50,
			Threshold:        0.5,
		},
	})
	if err != nil {
		log.Fatal(err)
	}

	logging.Info("[CircuitBreaker SlowRtRatio] Sentinel Go circuit breaking demo is running. You may see the pass/block metric in the metric log.")
	go func() {
		for {
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g1 blocked
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				if rand.Uint64()%20 > 9 {
					// Record current invocation as error.
					sentinel.TraceError(e, errors.New("biz error"))
				}
				// g1 passed
				time.Sleep(time.Duration(rand.Uint64()%80+10) * time.Millisecond)
				e.Exit()
			}
		}
	}()
	go func() {
		for {
			e, b := sentinel.Entry("abc")
			if b != nil {
				// g2 blocked
				time.Sleep(time.Duration(rand.Uint64()%20) * time.Millisecond)
			} else {
				// g2 passed
				time.Sleep(time.Duration(rand.Uint64()%80) * time.Millisecond)
				e.Exit()
			}
		}
	}()
	<-ch
}

在这里插入图片描述

六、gin集成sentinel

我们在goods_web中对grpc的GoodsList做限流：熔断跟限流差不多，只是配置不同而已，根据需求进行修改即可
goods_web/initialize/init_sentinel.go：初始化sentinel

package initialize

import (
	sentinel "github.com/alibaba/sentinel-golang/api"
	"github.com/alibaba/sentinel-golang/core/flow"
	"go.uber.org/zap"
)

func InitSentinel() {
	err := sentinel.InitDefault()
	if err != nil {
		zap.S().Fatalf("初始化sentinel 异常: %v", err)
	}

	//配置限流规则
	//这种配置应该从nacos中读取
	_, err = flow.LoadRules([]*flow.Rule{
		{
			Resource:               "goods-list",
			TokenCalculateStrategy: flow.Direct,
			ControlBehavior:        flow.Reject,
			//Threshold:              20,
			Threshold:        3, //为了测试，6秒钟只允许3个请求
			StatIntervalInMs: 6000,
		},
	})

	if err != nil {
		zap.S().Fatalf("加载规则失败: %v", err)
	}
}

goods_web/main.go：main中添加初始化逻辑

func main() {
	//1. 初始化logger
	initialize.InitLogger()
	//2. 初始化配置文件
	initialize.InitConfig()
	//3. 初始化routers
	Router := initialize.Routers()
	//4. 初始化翻译
	if err := initialize.InitTrans("zh"); err != nil {
		panic(err)
	}

	//5. 初始化srv的连接
	initialize.InitSrvConn()

	//6.初始化sentinel
	initialize.InitSentinel()

	//省略。。。

goods_web/api/goods/api_goods.go

func List(ctx *gin.Context) {
	//省略。。。
	e, b := sentinel.Entry("goods-list", sentinel.WithTrafficType(base.Inbound))
	if b != nil {
		ctx.JSON(http.StatusTooManyRequests, gin.H{
			"msg": "请求过于频繁，请稍后重试",
		})
		return
	}

	请求商品的service服务
	r, err := global.GoodsSrvClient.GoodsList(context.WithValue(context.Background(), "ginContext", ctx), request)
	if err != nil {
		zap.S().Errorw("[List] 查询 【商品列表】失败")
		api.HandleGrpcErrorToHttp(err, ctx)
		return
	}

	e.Exit()

	reMap := map[string]interface{}{
		"total": r.Total,
	}

在这里插入图片描述

36、熔断-限流-降级

目录

一、服务雪崩

二、熔断-限流-降级概述

三、熔断限流技术选型

四、sentinel限流

1 - 基于QPS限流

2 - Throttling策略

3 - sentinel预热/冷启动

五、sentinel熔断

1 - 熔断器模型

2 - 基于错误数熔断

3 - 基于错误率熔断

4 - 基于慢请求熔断

六、gin集成sentinel

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