traefik/pkg/server/service/loadbalancer/wrr/wrr.go

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package wrr
import (
"fmt"
"net/http"
"sync"
"github.com/containous/traefik/v2/pkg/config/dynamic"
"github.com/containous/traefik/v2/pkg/log"
)
type namedHandler struct {
http.Handler
name string
weight int
}
type stickyCookie struct {
name string
secure bool
httpOnly bool
}
// New creates a new load balancer.
func New(sticky *dynamic.Sticky) *Balancer {
balancer := &Balancer{
mutex: &sync.Mutex{},
index: -1,
}
if sticky != nil && sticky.Cookie != nil {
balancer.stickyCookie = &stickyCookie{
name: sticky.Cookie.Name,
secure: sticky.Cookie.Secure,
httpOnly: sticky.Cookie.HTTPOnly,
}
}
return balancer
}
// Balancer is a WeightedRoundRobin load balancer.
type Balancer struct {
handlers []*namedHandler
mutex *sync.Mutex
// Current index (starts from -1)
index int
currentWeight int
stickyCookie *stickyCookie
}
func (b *Balancer) maxWeight() int {
max := -1
for _, s := range b.handlers {
if s.weight > max {
max = s.weight
}
}
return max
}
func (b *Balancer) weightGcd() int {
divisor := -1
for _, s := range b.handlers {
if divisor == -1 {
divisor = s.weight
} else {
divisor = gcd(divisor, s.weight)
}
}
return divisor
}
func gcd(a, b int) int {
for b != 0 {
a, b = b, a%b
}
return a
}
func (b *Balancer) nextServer() (*namedHandler, error) {
b.mutex.Lock()
defer b.mutex.Unlock()
if len(b.handlers) == 0 {
return nil, fmt.Errorf("no servers in the pool")
}
// The algo below may look messy, but is actually very simple
// it calculates the GCD and subtracts it on every iteration, what interleaves servers
// and allows us not to build an iterator every time we readjust weights
// GCD across all enabled servers
gcd := b.weightGcd()
// Maximum weight across all enabled servers
max := b.maxWeight()
for {
b.index = (b.index + 1) % len(b.handlers)
if b.index == 0 {
b.currentWeight -= gcd
if b.currentWeight <= 0 {
b.currentWeight = max
if b.currentWeight == 0 {
return nil, fmt.Errorf("all servers have 0 weight")
}
}
}
srv := b.handlers[b.index]
if srv.weight >= b.currentWeight {
log.WithoutContext().Debugf("Service Select: %s", srv.name)
return srv, nil
}
}
}
func (b *Balancer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
if b.stickyCookie != nil {
cookie, err := req.Cookie(b.stickyCookie.name)
if err != nil && err != http.ErrNoCookie {
log.WithoutContext().Warnf("Error while reading cookie: %v", err)
}
if err == nil && cookie != nil {
for _, handler := range b.handlers {
if handler.name == cookie.Value {
handler.ServeHTTP(w, req)
return
}
}
}
}
server, err := b.nextServer()
if err != nil {
http.Error(w, http.StatusText(http.StatusInternalServerError)+err.Error(), http.StatusInternalServerError)
return
}
if b.stickyCookie != nil {
cookie := &http.Cookie{Name: b.stickyCookie.name, Value: server.name, Path: "/", HttpOnly: b.stickyCookie.httpOnly, Secure: b.stickyCookie.secure}
http.SetCookie(w, cookie)
}
server.ServeHTTP(w, req)
}
// AddService adds a handler.
// It is not thread safe with ServeHTTP.
func (b *Balancer) AddService(name string, handler http.Handler, weight *int) {
w := 1
if weight != nil {
w = *weight
}
b.handlers = append(b.handlers, &namedHandler{Handler: handler, name: name, weight: w})
}