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