Rework servers load-balancer to use the WRR

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

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

@@ -4,7 +4,6 @@ import (
 	"container/heap"
 	"context"
 	"errors"
-	"fmt"
 	"net/http"
 	"sync"
 
@@ -39,7 +38,7 @@ type Balancer struct {
 	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 AddService, and it is later removed or added to the map as needed,
+	// 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
@@ -48,10 +47,10 @@ type Balancer struct {
 }
 
 // New creates a new load balancer.
-func New(sticky *dynamic.Sticky, hc *dynamic.HealthCheck) *Balancer {
+func New(sticky *dynamic.Sticky, wantHealthCheck bool) *Balancer {
 	balancer := &Balancer{
 		status:           make(map[string]struct{}),
-		wantsHealthCheck: hc != nil,
+		wantsHealthCheck: wantHealthCheck,
 	}
 	if sticky != nil && sticky.Cookie != nil {
 		balancer.stickyCookie = &stickyCookie{
@@ -150,10 +149,7 @@ 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")
-	}
-	if len(b.status) == 0 {
+	if len(b.handlers) == 0 || len(b.status) == 0 {
 		return nil, errNoAvailableServer
 	}
 
@@ -223,9 +219,9 @@ func (b *Balancer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	server.ServeHTTP(w, req)
 }
 
-// AddService adds a handler.
+// Add adds a handler.
 // A handler with a non-positive weight is ignored.
-func (b *Balancer) AddService(name string, handler http.Handler, weight *int) {
+func (b *Balancer) Add(name string, handler http.Handler, weight *int) {
 	w := 1
 	if weight != nil {
 		w = *weight