Add apiserver metric for number of requests dropped by 'inflight-request' filters.

staging/src/k8s.io/apiserver/pkg/endpoints/metrics/metrics.go

@@ -78,9 +78,24 @@ var (
 		},
 		[]string{"verb", "resource", "subresource", "scope"},
 	)
+	// DroppedRequests is a number of requests dropped with 'Try again later' reponse"
+	DroppedRequests = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "apiserver_dropped_requests",
+			Help: "Number of requests dropped with 'Try again later' reponse",
+		},
+		[]string{"requestKind"},
+	)
 	kubectlExeRegexp = regexp.MustCompile(`^.*((?i:kubectl\.exe))`)
 )
 
+const (
+	// ReadOnlyKind is a string identifying read only request kind
+	ReadOnlyKind = "readOnly"
+	// MutatingKind is a string identifying mutating request kind
+	MutatingKind = "mutating"
+)
+
 func init() {
 	// Register all metrics.
 	prometheus.MustRegister(requestCounter)
@@ -88,6 +103,7 @@ func init() {
 	prometheus.MustRegister(requestLatencies)
 	prometheus.MustRegister(requestLatenciesSummary)
 	prometheus.MustRegister(responseSizes)
+	prometheus.MustRegister(DroppedRequests)
 }
 
 // Record records a single request to the standard metrics endpoints. For use by handlers that perform their own

staging/src/k8s.io/apiserver/pkg/server/filters/maxinflight.go

@@ -79,7 +79,8 @@ func WithMaxInFlightLimit(
 		}
 
 		var c chan bool
-		if !nonMutatingRequestVerbs.Has(requestInfo.Verb) {
+		isMutatingRequest := !nonMutatingRequestVerbs.Has(requestInfo.Verb)
+		if isMutatingRequest {
 			c = mutatingChan
 		} else {
 			c = nonMutatingChan
@@ -95,6 +96,12 @@ func WithMaxInFlightLimit(
 				handler.ServeHTTP(w, r)
 
 			default:
+				// We need to split this data between buckets used for throttling.
+				if isMutatingRequest {
+					metrics.DroppedRequests.WithLabelValues(metrics.MutatingKind).Inc()
+				} else {
+					metrics.DroppedRequests.WithLabelValues(metrics.ReadOnlyKind).Inc()
+				}
 				// at this point we're about to return a 429, BUT not all actors should be rate limited.  A system:master is so powerful
 				// that he should always get an answer.  It's a super-admin or a loopback connection.
 				if currUser, ok := apirequest.UserFrom(ctx); ok {