package util

import (
    "fmt"
    "hash/crc32"
    "math/rand"
    "sort"
    "time"
)

type HttpServer struct { //目标server类
    Host      string
    Weight    int
    CWeight   int    //当前权重
    Status    string //健康检查
    FailCount int    //计数器，默认是0
    SuccessCount int //检查到连续成功，当连续成功的次数达到这个值，把宕机的的机器的FailCount立刻重置为0，加快服务器启动速度
}

type HttpServers []*HttpServer

func (p HttpServers) Len() int           { return len(p) }
func (p HttpServers) Less(i, j int) bool { return p[i].CWeight > p[j].CWeight }
func (p HttpServers) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }

func NewHttpServer(host string, weight int) *HttpServer {
    return &HttpServer{Host: host, Weight: weight, CWeight: 0}
}

type LoadBalance struct { //负载均衡类
    Servers  HttpServers
    CurIndex int //指向当前访问的服务器
}

func NewLoadBalance() *LoadBalance {
    return &LoadBalance{Servers: make([]*HttpServer, 0)}
}

func (this *LoadBalance) AddServer(server *HttpServer) {
    this.Servers = append(this.Servers, server)
}

func (this *LoadBalance) SelectForRand() *HttpServer {
    rand.Seed(time.Now().UnixNano())
    index := rand.Intn(len(this.Servers))
    fmt.Println(index)
    return this.Servers[index]
}

func (this *LoadBalance) SelectByIpHash(ip string) *HttpServer {
    index := int(crc32.ChecksumIEEE([]byte(ip))) % len(this.Servers) //通过取余永远index都不会大于this.servers的长度
    return this.Servers[index]
}

func (this *LoadBalance) SelectByWeight(ip string) *HttpServer { //加权随机算法
    rand.Seed(time.Now().UnixNano())
    index := rand.Intn(len(ServerIndices)) //这里因为权重表为15个1和5个0组成，所以产生0到19的随机数
    fmt.Println(this.Servers[ServerIndices[index]])
    return this.Servers[ServerIndices[index]] //通过随机数的索引获得服务器索引进而获得地址
}

func (this *LoadBalance) SelectByWeightBetter(ip string) *HttpServer {
    rand.Seed(time.Now().UnixNano())
    sumList := make([]int, len(this.Servers))
    sum := 0
    for i := 0; i < len(this.Servers); i++ {
        sum += this.Servers[i].Weight
        sumList[i] = sum

    }
    _rand := rand.Intn(sum)
    for index, value := range sumList {
        if _rand < value {
            return this.Servers[index]
        }
    }
    return this.Servers[0]
}

func (this *LoadBalance) RoundRobin() *HttpServer {
    server := this.Servers[this.CurIndex]
    //this.CurIndex ++
    //if this.CurIndex >= len(this.Servers) {
    //    this.CurIndex = 0
    //}
    this.CurIndex = (this.CurIndex + 1) % len(this.Servers)
    if server.Status == "Down" { //如果当前节点宕机了，则递归查找可以用的服务器
        return this.RoundRobin()
    }
    return server
}

func (this *LoadBalance) RoundRobinByWeight() *HttpServer {
    server := this.Servers[ServerIndices[this.CurIndex]]
    this.CurIndex = (this.CurIndex + 1) % len(ServerIndices)
    return server
}

func (this *LoadBalance) RoundRobinByWeight2() *HttpServer { //加权轮询 ,使用区间算法
    server := this.Servers[0]
    sum := 0
    //3:1:1
    for i := 0; i < len(this.Servers); i++ {
        sum += this.Servers[i].Weight //第一次是3   [0,3)  [3,4)   [4,5)
        if this.CurIndex < sum {
            server = this.Servers[i]
            if this.CurIndex == sum-1 && i != len(this.Servers)-1 {
                this.CurIndex++
            } else {
                this.CurIndex = (this.CurIndex + 1) % sum //这里是重要的一步
            }
            fmt.Println(this.CurIndex)
            break
        }
    }
    return server
}

func (this *LoadBalance) RoundRobinByWeight3() *HttpServer { //平滑加权轮询
    for _, s := range this.Servers {
        s.CWeight = s.CWeight + s.Weight
    }
    sort.Sort(this.Servers)
    max := this.Servers[0]

    max.CWeight = max.CWeight - SumWeight
    return max
}

var LB *LoadBalance
var ServerIndices []int
var SumWeight int

func checkServers(servers HttpServers)  {
    t:= time.NewTicker(time.Second*3)
    check:=NewHtttpChecker(servers)
    for {
        select{
        case <- t.C:
            check.Check(time.Second*2)
            for _,s:=range servers{
                fmt.Println(s.Host,s.Status,s.FailCount)
            }
            fmt.Println("---------------------------------")
        }
    }
}

func init() {
    LB = NewLoadBalance()
    LB.AddServer(NewHttpServer("http://localhost:12346", 3)) //web1
    LB.AddServer(NewHttpServer("http://localhost:12347", 1)) //web2
    LB.AddServer(NewHttpServer("http://localhost:12348", 1)) //web2
    for index, server := range LB.Servers {
        if server.Weight > 0 {
            for i := 0; i < server.Weight; i++ {
                ServerIndices = append(ServerIndices, index)
            }
        }
        SumWeight = SumWeight + server.Weight //计算加权总和
    }
    go checkServers(LB.Servers)

    //fmt.Println(ServerIndices)
}

package util

import (
    "net/http"
    "time"
)

type HttpChecker struct {
    Servers    HttpServers
    FailMax    int
    RecovCount int //连续成功到达这个值，就会被标识为UP
}

func NewHtttpChecker(servers HttpServers) *HttpChecker {
    return &HttpChecker{Servers: servers, FailMax: 6, RecovCount: 3}
}
func (this *HttpChecker) Check(timeout time.Duration) {
    client := http.Client{}
    for _, server := range this.Servers {
        res, err := client.Head(server.Host)
        if res != nil {
            defer res.Body.Close()
        }
        if err != nil { //宕机了
            this.Fail(server)
            continue
        }
        if res.StatusCode >= 200 && res.StatusCode < 400 {
            this.Success(server)
        } else {
            this.Fail(server)
        }
    }
}

func (this *HttpChecker) Fail(server *HttpServer) {
    if server.FailCount >= this.FailMax { //超过阈值
        server.Status = "DOWN"
    } else {
        server.FailCount++
    }
    server.SuccessCount = 0

}

func (this *HttpChecker) Success(server *HttpServer) {
    if server.FailCount > 0 {
        server.FailCount--
        server.SuccessCount++
        if server.SuccessCount == this.RecovCount {
            server.FailCount = 0
            server.Status = "UP"
            server.SuccessCount = 0
        }
    } else {
        server.Status = "UP"
    }

}

来自为知笔记(Wiz)