From b33e8187851cace587184f73941a53da0f75098e Mon Sep 17 00:00:00 2001
From: Lukasz Szaszkiewicz <lukasz.szaszkiewicz@gmail.com>
Date: Thu, 9 Mar 2023 14:11:59 +0100
Subject: [PATCH] reflector: use watchlist

Kubernetes-commit: 51ec7305aa9fc2541c46c4836f5e150c818341f9
---
 tools/cache/reflector.go | 39 +++++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/tools/cache/reflector.go b/tools/cache/reflector.go
index 69fc23a1..7363ce35 100644
--- a/tools/cache/reflector.go
+++ b/tools/cache/reflector.go
@@ -100,6 +100,15 @@ type Reflector struct {
 	ShouldResync func() bool
 	// MaxInternalErrorRetryDuration defines how long we should retry internal errors returned by watch.
 	MaxInternalErrorRetryDuration time.Duration
+	// UseWatchList if turned on instructs the reflector to open a stream to bring data from the API server.
+	// Streaming has the primary advantage of using fewer server's resources to fetch data.
+	//
+	// The old behaviour establishes a LIST request which gets data in chunks.
+	// Paginated list is less efficient and depending on the actual size of objects
+	// might result in an increased memory consumption of the APIServer.
+	//
+	// See https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/3157-watch-list#design-details
+	UseWatchList bool
 }
 
 // ResourceVersionUpdater is an interface that allows store implementation to
@@ -312,17 +321,39 @@ func (r *Reflector) resyncChan() (<-chan time.Time, func() bool) {
 // It returns error if ListAndWatch didn't even try to initialize watch.
 func (r *Reflector) ListAndWatch(stopCh <-chan struct{}) error {
 	klog.V(3).Infof("Listing and watching %v from %s", r.typeDescription, r.name)
+	var err error
+	var w watch.Interface
+	fallbackToList := !r.UseWatchList
 
-	err := r.list(stopCh)
-	if err != nil {
-		return err
+	if r.UseWatchList {
+		w, err = r.watchList(stopCh)
+		if w == nil && err == nil {
+			// stopCh was closed
+			return nil
+		}
+		if err != nil {
+			if !apierrors.IsInvalid(err) {
+				return err
+			}
+			klog.Warning("the watch-list feature is not supported by the server, falling back to the previous LIST/WATCH semantic")
+			fallbackToList = true
+			// Ensure that we won't accidentally pass some garbage down the watch.
+			w = nil
+		}
+	}
+
+	if fallbackToList {
+		err = r.list(stopCh)
+		if err != nil {
+			return err
+		}
 	}
 
 	resyncerrc := make(chan error, 1)
 	cancelCh := make(chan struct{})
 	defer close(cancelCh)
 	go r.startResync(stopCh, cancelCh, resyncerrc)
-	return r.watch(nil, stopCh, resyncerrc)
+	return r.watch(w, stopCh, resyncerrc)
 }
 
 // startResync periodically calls r.store.Resync() method.