Add 'apiserver_watch_events_sizes'.

That metric can be used to estimate the size of watch events sent out to
the clients.

Kubernetes-commit: 4af189aab9cca61d1a701133596f6f82b1ca0719

pkg/endpoints/handlers/watch.go

@@ -238,6 +238,7 @@ func (s *WatchServer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 			// type
 			unknown.Raw = buf.Bytes()
 			event.Object = &unknown
+			metrics.WatchEventsSizes.WithLabelValues(kind.Group, kind.Version, kind.Kind).Observe(float64(len(unknown.Raw)))
 
 			*outEvent = metav1.WatchEvent{}
 

pkg/endpoints/metrics/metrics.go

@@ -148,6 +148,14 @@ var (
 		},
 		[]string{"group", "version", "kind"},
 	)
+	WatchEventsSizes = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "apiserver_watch_events_sizes",
+			Help:    "Watch event size distribution in bytes",
+			Buckets: prometheus.ExponentialBuckets(1024, 2.0, 8), // 1K, 2K, 4K, 8K, ..., 128K.
+		},
+		[]string{"group", "version", "kind"},
+	)
 	// Because of volatality of the base metric this is pre-aggregated one. Instead of reporing current usage all the time
 	// it reports maximal usage during the last second.
 	currentInflightRequests = prometheus.NewGaugeVec(
@@ -171,6 +179,7 @@ var (
 		DeprecatedDroppedRequests,
 		RegisteredWatchers,
 		WatchEvents,
+		WatchEventsSizes,
 		currentInflightRequests,
 	}
 )