Make the loadbalancers servers order random

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
Co-authored-by: Romain <rtribotte@users.noreply.github.com>

pkg/server/service/service.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"math/rand"
 	"net/http"
 	"net/http/httputil"
 	"net/url"
@@ -51,6 +52,7 @@ func NewManager(configs map[string]*runtime.ServiceInfo, metricsRegistry metrics
 		roundTripperManager: roundTripperManager,
 		balancers:           make(map[string]healthcheck.Balancers),
 		configs:             configs,
+		rand:                rand.New(rand.NewSource(time.Now().UnixNano())),
 	}
 }
 
@@ -66,6 +68,7 @@ type Manager struct {
 	// which is why there is not just one Balancer per service name.
 	balancers map[string]healthcheck.Balancers
 	configs   map[string]*runtime.ServiceInfo
+	rand      *rand.Rand // For the initial shuffling of load-balancers.
 }
 
 // BuildHTTP Creates a http.Handler for a service configuration.
@@ -212,7 +215,7 @@ func (m *Manager) getWRRServiceHandler(ctx context.Context, serviceName string,
 	}
 
 	balancer := wrr.New(config.Sticky, config.HealthCheck)
-	for _, service := range config.Services {
+	for _, service := range shuffle(config.Services, m.rand) {
 		serviceHandler, err := m.BuildHTTP(ctx, service.Name)
 		if err != nil {
 			return nil, err
@@ -414,7 +417,7 @@ func (m *Manager) getLoadBalancer(ctx context.Context, serviceName string, servi
 func (m *Manager) upsertServers(ctx context.Context, lb healthcheck.BalancerHandler, servers []dynamic.Server) error {
 	logger := log.FromContext(ctx)
 
-	for name, srv := range servers {
+	for name, srv := range shuffle(servers, m.rand) {
 		u, err := url.Parse(srv.URL)
 		if err != nil {
 			return fmt.Errorf("error parsing server URL %s: %w", srv.URL, err)
@@ -443,3 +446,11 @@ func convertSameSite(sameSite string) http.SameSite {
 		return 0
 	}
 }
+
+func shuffle[T any](values []T, r *rand.Rand) []T {
+	shuffled := make([]T, len(values))
+	copy(shuffled, values)
+	r.Shuffle(len(shuffled), func(i, j int) { shuffled[i], shuffled[j] = shuffled[j], shuffled[i] })
+
+	return shuffled
+}