balancer/weightedroundrobin: Add recording point for endpoint weight not yet usable and add metrics tests

balancer/weightedroundrobin/balancer.go

@@ -415,7 +415,7 @@ func (p *picker) inc() uint32 {
 }
 
 func (p *picker) regenerateScheduler() {
-	s := p.newScheduler()
+	s := p.newScheduler(true)
 	atomic.StorePointer(&p.scheduler, unsafe.Pointer(&s))
 }
 
@@ -558,14 +558,17 @@ func (w *weightedSubConn) updateConnectivityState(cs connectivity.State) connect
 		w.SubConn.Connect()
 	case connectivity.Ready:
 		// If we transition back to READY state, reset nonEmptySince so that we
-		// apply the blackout period after we start receiving load data.  Note
-		// that we cannot guarantee that we will never receive lingering
-		// callbacks for backend metric reports from the previous connection
-		// after the new connection has been established, but they should be
-		// masked by new backend metric reports from the new connection by the
-		// time the blackout period ends.
+		// apply the blackout period after we start receiving load data. Also
+		// reset lastUpdated to trigger endpoint weight not yet usable in the
+		// case endpoint gets asked what weight it is before receiving a new
+		// load report. Note that we cannot guarantee that we will never receive
+		// lingering callbacks for backend metric reports from the previous
+		// connection after the new connection has been established, but they
+		// should be masked by new backend metric reports from the new
+		// connection by the time the blackout period ends.
 		w.mu.Lock()
 		w.nonEmptySince = time.Time{}
+		w.lastUpdated = time.Time{}
 		w.mu.Unlock()
 	case connectivity.Shutdown:
 		if w.stopORCAListener != nil {
@@ -592,7 +595,7 @@ func (w *weightedSubConn) updateConnectivityState(cs connectivity.State) connect
 // account the parameters.  Returns 0 for blacked out or expired data, which
 // will cause the backend weight to be treated as the mean of the weights of the
 // other backends. If forScheduler is set to true, this function will emit
-// metrics through the mtrics registry.
+// metrics through the metrics registry.
 func (w *weightedSubConn) weight(now time.Time, weightExpirationPeriod, blackoutPeriod time.Duration, recordMetrics bool) (weight float64) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
@@ -603,6 +606,13 @@ func (w *weightedSubConn) weight(now time.Time, weightExpirationPeriod, blackout
 		}()
 	}
 
+	// The SubConn has not received a load report (i.e. just turned READY with
+	// no load report).
+	if w.lastUpdated == (time.Time{}) {
+		endpointWeightNotYetUsableMetric.Record(w.metricsRecorder, 1, w.target, w.locality)
+		return 0
+	}
+
 	// If the most recent update was longer ago than the expiration period,
 	// reset nonEmptySince so that we apply the blackout period again if we
 	// start getting data again in the future, and return 0.

balancer/weightedroundrobin/balancer_test.go

@@ -32,6 +32,7 @@ import (
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/stubserver"
 	"google.golang.org/grpc/internal/testutils/roundrobin"
+	"google.golang.org/grpc/internal/testutils/stats"
 	"google.golang.org/grpc/orca"
 	"google.golang.org/grpc/peer"
 	"google.golang.org/grpc/resolver"
@@ -81,6 +82,14 @@ var (
 		WeightUpdatePeriod:      stringp(".050s"),
 		ErrorUtilizationPenalty: float64p(0),
 	}
+	testMetricsConfig = iwrr.LBConfig{
+		EnableOOBLoadReport:     boolp(false),
+		OOBReportingPeriod:      stringp("0.005s"),
+		BlackoutPeriod:          stringp("0s"),
+		WeightExpirationPeriod:  stringp("60s"),
+		WeightUpdatePeriod:      stringp(".050s"),
+		ErrorUtilizationPenalty: float64p(0),
+	}
 )
 
 type testServer struct {
@@ -196,6 +205,43 @@ func (s) TestBalancer_OneAddress(t *testing.T) {
 	}
 }
 
+// TestWRRMetricsBasic tests metrics emitted from the WRR balancer. It
+// configures a weighted round robin balancer as the top level balancer of a
+// ClientConn, and configures a fake stats handler on the ClientConn to receive
+// metrics. It verifies stats emitted from the Weighted Round Robin Balancer on
+// balancer startup case which triggers the first picker and scheduler update
+// before any load reports are received.
+//
+// Note that this test and others, metrics emission asssertions are a snapshot
+// of the most recently emitted metrics. This is due to the nondeterminism of
+// scheduler updates with respect to test bodies, so the assertions made are
+// from the most recently synced state of the system (picker/scheduler) from the
+// test body.
+func (s) TestWRRMetricsBasic(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+
+	srv := startServer(t, reportCall)
+	sc := svcConfig(t, testMetricsConfig)
+
+	mr := stats.NewTestMetricsRecorder(t)
+	if err := srv.StartClient(grpc.WithDefaultServiceConfig(sc), grpc.WithStatsHandler(mr)); err != nil {
+		t.Fatalf("Error starting client: %v", err)
+	}
+	srv.callMetrics.SetQPS(float64(1))
+
+	if _, err := srv.Client.EmptyCall(ctx, &testpb.Empty{}); err != nil {
+		t.Fatalf("Error from EmptyCall: %v", err)
+	}
+
+	mr.AssertDataForMetric("grpc.lb.wrr.rr_fallback", 1)           // Falls back because only one SubConn.
+	mr.AssertDataForMetric("grpc.lb.wrr.endpoint_weight_stale", 0) // The endpoint weight has not expired so this is 0 (never emitted).
+	mr.AssertDataForMetric("grpc.lb.wrr.endpoint_weight_not_yet_usable", 1)
+	// Unusable, so no endpoint weight. Due to only one SubConn, this will never
+	// update the weight. Thus, this will stay 0.
+	mr.AssertDataForMetric("grpc.lb.wrr.endpoint_weights", 0)
+}
+
 // Tests two addresses with ORCA reporting disabled (should fall back to pure
 // RR).
 func (s) TestBalancer_TwoAddresses_ReportingDisabled(t *testing.T) {

balancer/weightedroundrobin/metrics_test.go

@@ -0,0 +1,163 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package weightedroundrobin
+
+import (
+	"testing"
+	"time"
+
+	"google.golang.org/grpc/internal/grpctest"
+	iserviceconfig "google.golang.org/grpc/internal/serviceconfig"
+	"google.golang.org/grpc/internal/testutils/stats"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+// TestWRR_Metrics_SubConnWeight tests different scenarios for the weight call
+// on a weighted SubConn, and expects certain metrics for each of these
+// scenarios.
+func (s) TestWRR_Metrics_SubConnWeight(t *testing.T) {
+	tests := []struct {
+		name                           string
+		weightExpirationPeriod         time.Duration
+		blackoutPeriod                 time.Duration
+		lastUpdated                    time.Time
+		nonEmpty                       time.Time
+		nowTime                        time.Time
+		endpointWeightStaleWant        float64
+		endpointWeightNotYetUsableWant float64
+		endpointWeightWant             float64
+	}{
+		// The weighted SubConn's lastUpdated field hasn't been set, so this
+		// SubConn's weight is not yet usable. Thus, should emit that endpoint
+		// weight is not yet usable, and 0 for weight.
+		{
+			name:                           "no weight set",
+			weightExpirationPeriod:         time.Second,
+			blackoutPeriod:                 time.Second,
+			nowTime:                        time.Now(),
+			endpointWeightStaleWant:        0,
+			endpointWeightNotYetUsableWant: 1,
+			endpointWeightWant:             0,
+		},
+		{
+			name:                           "weight expiration",
+			lastUpdated:                    time.Now(),
+			weightExpirationPeriod:         2 * time.Second,
+			blackoutPeriod:                 time.Second,
+			nowTime:                        time.Now().Add(100 * time.Second),
+			endpointWeightStaleWant:        1,
+			endpointWeightNotYetUsableWant: 0,
+			endpointWeightWant:             0,
+		},
+		{
+			name:                           "in blackout period",
+			lastUpdated:                    time.Now(),
+			weightExpirationPeriod:         time.Minute,
+			blackoutPeriod:                 10 * time.Second,
+			nowTime:                        time.Now(),
+			endpointWeightStaleWant:        0,
+			endpointWeightNotYetUsableWant: 1,
+			endpointWeightWant:             0,
+		},
+		{
+			name:                           "normal weight",
+			lastUpdated:                    time.Now(),
+			nonEmpty:                       time.Now(),
+			weightExpirationPeriod:         time.Minute,
+			blackoutPeriod:                 time.Second,
+			nowTime:                        time.Now().Add(10 * time.Second),
+			endpointWeightStaleWant:        0,
+			endpointWeightNotYetUsableWant: 0,
+			endpointWeightWant:             3,
+		},
+		{
+			name:                           "weight expiration takes precdedence over blackout",
+			lastUpdated:                    time.Now(),
+			nonEmpty:                       time.Now(),
+			weightExpirationPeriod:         time.Second,
+			blackoutPeriod:                 time.Minute,
+			nowTime:                        time.Now().Add(10 * time.Second),
+			endpointWeightStaleWant:        1,
+			endpointWeightNotYetUsableWant: 0,
+			endpointWeightWant:             0,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			tmr := stats.NewTestMetricsRecorder(t)
+			wsc := &weightedSubConn{
+				metricsRecorder: tmr,
+				weightVal:       3,
+				lastUpdated:     test.lastUpdated,
+				nonEmptySince:   test.nonEmpty,
+			}
+			wsc.weight(test.nowTime, test.weightExpirationPeriod, test.blackoutPeriod, true)
+
+			tmr.AssertDataForMetric("grpc.lb.wrr.endpoint_weight_stale", test.endpointWeightStaleWant)
+			tmr.AssertDataForMetric("grpc.lb.wrr.endpoint_weight_not_yet_usable", test.endpointWeightNotYetUsableWant)
+			tmr.AssertDataForMetric("grpc.lb.wrr.endpoint_weights", test.endpointWeightWant)
+		})
+	}
+
+}
+
+// TestWRR_Metrics_Scheduler_RR_Fallback tests the round robin fallback metric
+// for scheduler updates. It tests the case with one SubConn, and two SubConns
+// with no weights. Both of these should emit a count metric for round robin
+// fallback.
+func (s) TestWRR_Metrics_Scheduler_RR_Fallback(t *testing.T) {
+	tmr := stats.NewTestMetricsRecorder(t)
+	wsc := &weightedSubConn{
+		metricsRecorder: tmr,
+		weightVal:       0,
+	}
+
+	p := &picker{
+		cfg: &lbConfig{
+			BlackoutPeriod:         iserviceconfig.Duration(10 * time.Second),
+			WeightExpirationPeriod: iserviceconfig.Duration(3 * time.Minute),
+		},
+		subConns:        []*weightedSubConn{wsc},
+		metricsRecorder: tmr,
+	}
+	// There is only one SubConn, so no matter if the SubConn has a weight or
+	// not will fallback to round robin.
+	p.regenerateScheduler()
+	tmr.AssertDataForMetric("grpc.lb.wrr.rr_fallback", 1)
+	tmr.ClearMetrics()
+
+	// With two SubConns, if neither of them have weights, it will also fallback
+	// to round robin.
+	wsc2 := &weightedSubConn{
+		target:          "target",
+		metricsRecorder: tmr,
+		weightVal:       0,
+	}
+	p.subConns = append(p.subConns, wsc2)
+	p.regenerateScheduler()
+	tmr.AssertDataForMetric("grpc.lb.wrr.rr_fallback", 1)
+}

balancer/weightedroundrobin/scheduler.go

@@ -31,14 +31,16 @@ type scheduler interface {
 // len(scWeights)-1 are zero or there is only a single subconn, otherwise it
 // will return an Earliest Deadline First (EDF) scheduler implementation that
 // selects the subchannels according to their weights.
-func (p *picker) newScheduler() scheduler {
-	scWeights := p.scWeights(true)
+func (p *picker) newScheduler(recordMetrics bool) scheduler {
+	scWeights := p.scWeights(recordMetrics)
 	n := len(scWeights)
 	if n == 0 {
 		return nil
 	}
 	if n == 1 {
-		rrFallbackMetric.Record(p.metricsRecorder, 1, p.target, p.locality)
+		if recordMetrics {
+			rrFallbackMetric.Record(p.metricsRecorder, 1, p.target, p.locality)
+		}
 		return &rrScheduler{numSCs: 1, inc: p.inc}
 	}
 	sum := float64(0)
@@ -55,7 +57,9 @@ func (p *picker) newScheduler() scheduler {
 	}
 
 	if numZero >= n-1 {
-		rrFallbackMetric.Record(p.metricsRecorder, 1, p.target, p.locality)
+		if recordMetrics {
+			rrFallbackMetric.Record(p.metricsRecorder, 1, p.target, p.locality)
+		}
 		return &rrScheduler{numSCs: uint32(n), inc: p.inc}
 	}
 	unscaledMean := sum / float64(n-numZero)

internal/stats/metrics_recorder_list_test.go

@@ -144,8 +144,8 @@ func (s) TestMetricsRecorderList(t *testing.T) {
 
 	// Create two stats.Handlers which also implement MetricsRecorder, configure
 	// one as a global dial option and one as a local dial option.
-	mr1 := stats.NewTestMetricsRecorder(t, []string{})
-	mr2 := stats.NewTestMetricsRecorder(t, []string{})
+	mr1 := stats.NewTestMetricsRecorder(t)
+	mr2 := stats.NewTestMetricsRecorder(t)
 
 	defer internal.ClearGlobalDialOptions()
 	internal.AddGlobalDialOptions.(func(opt ...grpc.DialOption))(grpc.WithStatsHandler(mr1))