Debounce kubernetes service endpoint updates

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
(cherry picked from commit 2992477c4b)
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

pkg/agent/tunnel/tunnel.go

@@ -35,6 +35,10 @@ import (
 	"k8s.io/kubernetes/pkg/cluster/ports"
 )
 
+var (
+	endpointDebounceDelay = time.Second
+)
+
 type agentTunnel struct {
 	client      kubernetes.Interface
 	cidrs       cidranger.Ranger
@@ -306,9 +310,14 @@ func (a *agentTunnel) watchEndpoints(ctx context.Context, apiServerReady <-chan
 		<-done
 	}()
 
+	var cancelUpdate context.CancelFunc
+
 	for {
 		select {
 		case <-ctx.Done():
+			if cancelUpdate != nil {
+				cancelUpdate()
+			}
 			return
 		case ev, ok := <-watch.ResultChan():
 			endpoint, ok := ev.Object.(*v1.Endpoints)
@@ -317,9 +326,29 @@ func (a *agentTunnel) watchEndpoints(ctx context.Context, apiServerReady <-chan
 				continue
 			}
 
+			if cancelUpdate != nil {
+				cancelUpdate()
+			}
+
+			var debounceCtx context.Context
+			debounceCtx, cancelUpdate = context.WithCancel(ctx)
+
+			// When joining the cluster, the apiserver adds, removes, and then readds itself to
+			// the endpoint list several times.  This causes a bit of thrashing if we react to
+			// endpoint changes immediately.  Instead, perform the endpoint update in a
+			// goroutine that sleeps for a short period before checking for changes and updating
+			// the proxy addresses.  If another update occurs, the previous update operation
+			// will be cancelled and a new one queued.
+			go func() {
+				select {
+				case <-time.After(endpointDebounceDelay):
+				case <-debounceCtx.Done():
+					return
+				}
+
 				newAddresses := util.GetAddresses(endpoint)
 				if reflect.DeepEqual(newAddresses, proxy.SupervisorAddresses()) {
-				continue
+					return
 				}
 				proxy.Update(newAddresses)
 
@@ -339,6 +368,7 @@ func (a *agentTunnel) watchEndpoints(ctx context.Context, apiServerReady <-chan
 						logrus.Infof("Stopped tunnel to %s", address)
 					}
 				}
+			}()
 		}
 	}
 }