traefik/pkg/server/service/loadbalancer/wrr/wrr.go
2021-03-04 09:02:03 +01:00

157 lines
3.9 KiB
Go

package wrr
import (
"container/heap"
"errors"
"fmt"
"net/http"
"sync"
"github.com/traefik/traefik/v2/pkg/config/dynamic"
"github.com/traefik/traefik/v2/pkg/log"
)
type namedHandler struct {
http.Handler
name string
weight float64
deadline float64
}
type stickyCookie struct {
name string
secure bool
httpOnly bool
}
// Balancer is a WeightedRoundRobin load balancer based on Earliest Deadline First (EDF).
// (https://en.wikipedia.org/wiki/Earliest_deadline_first_scheduling)
// Each pick from the schedule has the earliest deadline entry selected.
// Entries have deadlines set at currentDeadline + 1 / weight,
// providing weighted round robin behavior with floating point weights and an O(log n) pick time.
type Balancer struct {
stickyCookie *stickyCookie
mutex sync.RWMutex
handlers []*namedHandler
curDeadline float64
}
// New creates a new load balancer.
func New(sticky *dynamic.Sticky) *Balancer {
balancer := &Balancer{}
if sticky != nil && sticky.Cookie != nil {
balancer.stickyCookie = &stickyCookie{
name: sticky.Cookie.Name,
secure: sticky.Cookie.Secure,
httpOnly: sticky.Cookie.HTTPOnly,
}
}
return balancer
}
// Len implements heap.Interface/sort.Interface.
func (b *Balancer) Len() int { return len(b.handlers) }
// Less implements heap.Interface/sort.Interface.
func (b *Balancer) Less(i, j int) bool {
return b.handlers[i].deadline < b.handlers[j].deadline
}
// Swap implements heap.Interface/sort.Interface.
func (b *Balancer) Swap(i, j int) {
b.handlers[i], b.handlers[j] = b.handlers[j], b.handlers[i]
}
// Push implements heap.Interface for pushing an item into the heap.
func (b *Balancer) Push(x interface{}) {
h, ok := x.(*namedHandler)
if !ok {
return
}
b.handlers = append(b.handlers, h)
}
// Pop implements heap.Interface for poping an item from the heap.
// It panics if b.Len() < 1.
func (b *Balancer) Pop() interface{} {
h := b.handlers[len(b.handlers)-1]
b.handlers = b.handlers[0 : len(b.handlers)-1]
return h
}
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")
}
// Pick handler with closest deadline.
handler := heap.Pop(b).(*namedHandler)
// curDeadline should be handler's deadline so that new added entry would have a fair competition environment with the old ones.
b.curDeadline = handler.deadline
handler.deadline += 1 / handler.weight
heap.Push(b, handler)
log.WithoutContext().Debugf("Service selected by WRR: %s", handler.name)
return handler, 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 && !errors.Is(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.
// A handler with a non-positive weight is ignored.
func (b *Balancer) AddService(name string, handler http.Handler, weight *int) {
w := 1
if weight != nil {
w = *weight
}
if w <= 0 { // non-positive weight is meaningless
return
}
h := &namedHandler{Handler: handler, name: name, weight: float64(w)}
// use RWLock to protect b.curDeadline
b.mutex.RLock()
h.deadline = b.curDeadline + 1/h.weight
b.mutex.RUnlock()
heap.Push(b, h)
}