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lb.go
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lb.go
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package loadbalance
import (
"errors"
"math/rand"
"sync"
"time"
log "github.com/Sirupsen/logrus"
)
var (
ErrEmpty = errors.New("not backend addresses")
ErrAllDown = errors.New("all backend servers down")
)
type Updater interface {
// update backend server addresses
Update() ([]string, error)
}
type BackendServer struct {
Addr string
FailCnt int
Down bool
DownTime time.Time
}
type LoadBalancer struct {
mu sync.Mutex
serverList []*BackendServer
serverIndex map[string]*BackendServer
next int
cnt int
lastUpdate time.Time
updateInterval time.Duration
updater Updater
updating bool
failThreshold int
activeCnt int
}
func NewLoadBalancer(u Updater, interval time.Duration, maxErr int, randStart bool) *LoadBalancer {
addrs, err := u.Update()
if err != nil {
log.Errorf("init backend addresses fail")
return nil
}
l := len(addrs)
index := make(map[string]*BackendServer)
servers := make([]*BackendServer, l, l)
for i := 0; i < l; i++ {
s := &BackendServer{
Addr: addrs[i],
FailCnt: 0,
Down: false,
}
servers[i] = s
index[addrs[i]] = s
}
next := 0
if randStart {
randNext := rand.Int31n(int32(l))
next = int(randNext)
}
lb := &LoadBalancer{
mu: sync.Mutex{},
serverList: servers,
serverIndex: index,
next: next,
cnt: l,
lastUpdate: time.Now(),
updateInterval: interval,
updater: u,
updating: false,
failThreshold: maxErr,
activeCnt: l,
}
return lb
}
func (lb *LoadBalancer) Get() (string, error) {
t := time.Now()
lb.mu.Lock()
defer lb.mu.Unlock()
if t.Sub(lb.lastUpdate) > lb.updateInterval && !lb.updating {
lb.updating = true
go func() {
addrs, err := lb.updater.Update()
if err != nil {
log.Errorf("update fail,err=%v", err)
lb.updating = false
} else {
lb.Set(addrs)
}
lb.lastUpdate = time.Now()
lb.updating = false
}()
}
if lb.cnt == 0 {
return "", ErrEmpty
}
if lb.activeCnt == 0 {
return "", ErrAllDown
}
if lb.next >= lb.cnt {
lb.next = 0
}
start := lb.next
for {
s := lb.serverList[lb.next]
lb.next = (lb.next + 1) % lb.cnt
if lb.next == start && lb.cnt > 1 {
return s.Addr, errors.New("no active server")
}
if !s.Down {
return s.Addr, nil
} else {
if t.Sub(s.DownTime) > lb.updateInterval*time.Duration(10) {
log.Infof("%s is mark as active", s.Addr)
s.Down = false
}
return s.Addr, nil
}
}
}
func (lb *LoadBalancer) Set(addrs []string) {
if len(addrs) == 0 {
log.Errorf("do not set zero length addrs")
}
m := make(map[string]int)
for _, addr := range addrs {
m[addr] = 1
}
lb.mu.Lock()
defer lb.mu.Unlock()
newList := []*BackendServer{}
for _, server := range lb.serverList {
_, ok := m[server.Addr]
if ok {
newList = append(newList, server)
delete(m, server.Addr)
} else {
delete(lb.serverIndex, server.Addr)
}
}
for k, _ := range m {
s := &BackendServer{
Addr: k,
FailCnt: 0,
Down: false,
}
newList = append(newList, s)
lb.serverIndex[k] = s
}
lb.cnt = len(newList)
lb.serverList = newList
if lb.next >= lb.cnt {
lb.next = 0
}
}
func (lb *LoadBalancer) MarkFail(addr string) {
lb.mu.Lock()
defer lb.mu.Unlock()
s, ok := lb.serverIndex[addr]
if ok {
s.FailCnt = s.FailCnt + 1
if s.FailCnt >= lb.failThreshold {
log.Infof("%s is marked as down", addr)
s.Down = true
s.DownTime = time.Now()
s.FailCnt = 0
lb.activeCnt = lb.activeCnt - 1
}
}
}