traefik/pkg/server/service/loadbalancer/wrr/wrr.go
2024-01-18 09:30:06 +01:00

280 lines
7 KiB
Go

package wrr
import (
"container/heap"
"context"
"errors"
"fmt"
"hash/fnv"
"net/http"
"sync"
"github.com/rs/zerolog/log"
"github.com/traefik/traefik/v3/pkg/config/dynamic"
)
type namedHandler struct {
http.Handler
name string
weight float64
deadline float64
}
type stickyCookie struct {
name string
secure bool
httpOnly bool
sameSite string
maxAge int
}
func convertSameSite(sameSite string) http.SameSite {
switch sameSite {
case "none":
return http.SameSiteNoneMode
case "lax":
return http.SameSiteLaxMode
case "strict":
return http.SameSiteStrictMode
default:
return http.SameSiteDefaultMode
}
}
// 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
wantsHealthCheck bool
handlersMu sync.RWMutex
// References all the handlers by name and also by the hashed value of the name.
handlerMap map[string]*namedHandler
handlers []*namedHandler
curDeadline float64
// status is a record of which child services of the Balancer are healthy, keyed
// by name of child service. A service is initially added to the map when it is
// created via Add, and it is later removed or added to the map as needed,
// through the SetStatus method.
status map[string]struct{}
// updaters is the list of hooks that are run (to update the Balancer
// parent(s)), whenever the Balancer status changes.
updaters []func(bool)
}
// New creates a new load balancer.
func New(sticky *dynamic.Sticky, wantHealthCheck bool) *Balancer {
balancer := &Balancer{
status: make(map[string]struct{}),
handlerMap: make(map[string]*namedHandler),
wantsHealthCheck: wantHealthCheck,
}
if sticky != nil && sticky.Cookie != nil {
balancer.stickyCookie = &stickyCookie{
name: sticky.Cookie.Name,
secure: sticky.Cookie.Secure,
httpOnly: sticky.Cookie.HTTPOnly,
sameSite: sticky.Cookie.SameSite,
maxAge: sticky.Cookie.MaxAge,
}
}
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 popping 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
}
// SetStatus sets on the balancer that its given child is now of the given
// status. balancerName is only needed for logging purposes.
func (b *Balancer) SetStatus(ctx context.Context, childName string, up bool) {
b.handlersMu.Lock()
defer b.handlersMu.Unlock()
upBefore := len(b.status) > 0
status := "DOWN"
if up {
status = "UP"
}
log.Ctx(ctx).Debug().Msgf("Setting status of %s to %v", childName, status)
if up {
b.status[childName] = struct{}{}
} else {
delete(b.status, childName)
}
upAfter := len(b.status) > 0
status = "DOWN"
if upAfter {
status = "UP"
}
// No Status Change
if upBefore == upAfter {
// We're still with the same status, no need to propagate
log.Ctx(ctx).Debug().Msgf("Still %s, no need to propagate", status)
return
}
// Status Change
log.Ctx(ctx).Debug().Msgf("Propagating new %s status", status)
for _, fn := range b.updaters {
fn(upAfter)
}
}
// RegisterStatusUpdater adds fn to the list of hooks that are run when the
// status of the Balancer changes.
// Not thread safe.
func (b *Balancer) RegisterStatusUpdater(fn func(up bool)) error {
if !b.wantsHealthCheck {
return errors.New("healthCheck not enabled in config for this weighted service")
}
b.updaters = append(b.updaters, fn)
return nil
}
var errNoAvailableServer = errors.New("no available server")
func (b *Balancer) nextServer() (*namedHandler, error) {
b.handlersMu.Lock()
defer b.handlersMu.Unlock()
if len(b.handlers) == 0 || len(b.status) == 0 {
return nil, errNoAvailableServer
}
var handler *namedHandler
for {
// 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)
if _, ok := b.status[handler.name]; ok {
break
}
}
log.Debug().Msgf("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.Warn().Err(err).Msg("Error while reading cookie")
}
if err == nil && cookie != nil {
b.handlersMu.RLock()
handler, ok := b.handlerMap[cookie.Value]
b.handlersMu.RUnlock()
if ok && handler != nil {
b.handlersMu.RLock()
_, isHealthy := b.status[handler.name]
b.handlersMu.RUnlock()
if isHealthy {
handler.ServeHTTP(w, req)
return
}
}
}
}
server, err := b.nextServer()
if err != nil {
if errors.Is(err, errNoAvailableServer) {
http.Error(w, errNoAvailableServer.Error(), http.StatusServiceUnavailable)
} else {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
return
}
if b.stickyCookie != nil {
cookie := &http.Cookie{
Name: b.stickyCookie.name,
Value: hash(server.name),
Path: "/",
HttpOnly: b.stickyCookie.httpOnly,
Secure: b.stickyCookie.secure,
SameSite: convertSameSite(b.stickyCookie.sameSite),
MaxAge: b.stickyCookie.maxAge,
}
http.SetCookie(w, cookie)
}
server.ServeHTTP(w, req)
}
// Add adds a handler.
// A handler with a non-positive weight is ignored.
func (b *Balancer) Add(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)}
b.handlersMu.Lock()
h.deadline = b.curDeadline + 1/h.weight
heap.Push(b, h)
b.status[name] = struct{}{}
b.handlerMap[name] = h
b.handlerMap[hash(name)] = h
b.handlersMu.Unlock()
}
func hash(input string) string {
hasher := fnv.New64()
// We purposely ignore the error because the implementation always returns nil.
_, _ = hasher.Write([]byte(input))
return fmt.Sprintf("%x", hasher.Sum64())
}