weightedtarget: return a more meaningful error when no child policy is reporting READY (#5391)

balancer/weightedtarget/weightedaggregator/aggregator.go

@@ -240,20 +240,23 @@ func (wbsa *Aggregator) BuildAndUpdate() {
 // Caller must hold wbsa.mu.
 func (wbsa *Aggregator) build() balancer.State {
 	wbsa.logger.Infof("Child pickers with config: %+v", wbsa.idToPickerState)
-	m := wbsa.idToPickerState
 	// TODO: use balancer.ConnectivityStateEvaluator to calculate the aggregated
 	// state.
 	var readyN, connectingN, idleN int
-	readyPickerWithWeights := make([]weightedPickerState, 0, len(m))
-	for _, ps := range m {
+	pickerN := len(wbsa.idToPickerState)
+	readyPickers := make([]weightedPickerState, 0, pickerN)
+	errorPickers := make([]weightedPickerState, 0, pickerN)
+	for _, ps := range wbsa.idToPickerState {
 		switch ps.stateToAggregate {
 		case connectivity.Ready:
 			readyN++
-			readyPickerWithWeights = append(readyPickerWithWeights, *ps)
+			readyPickers = append(readyPickers, *ps)
 		case connectivity.Connecting:
 			connectingN++
 		case connectivity.Idle:
 			idleN++
+		case connectivity.TransientFailure:
+			errorPickers = append(errorPickers, *ps)
 		}
 	}
 	var aggregatedState connectivity.State
@@ -272,11 +275,11 @@ func (wbsa *Aggregator) build() balancer.State {
 	var picker balancer.Picker
 	switch aggregatedState {
 	case connectivity.TransientFailure:
-		picker = base.NewErrPicker(balancer.ErrTransientFailure)
+		picker = newWeightedPickerGroup(errorPickers, wbsa.newWRR)
 	case connectivity.Connecting:
 		picker = base.NewErrPicker(balancer.ErrNoSubConnAvailable)
 	default:
-		picker = newWeightedPickerGroup(readyPickerWithWeights, wbsa.newWRR)
+		picker = newWeightedPickerGroup(readyPickers, wbsa.newWRR)
 	}
 	return balancer.State{ConnectivityState: aggregatedState, Picker: picker}
 }

balancer/weightedtarget/weightedtarget_test.go

@@ -20,7 +20,9 @@ package weightedtarget
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
+	"strings"
 	"testing"
 	"time"
 
@@ -569,7 +571,11 @@ func (s) TestWeightedTarget_TwoSubBalancers_MoreBackends(t *testing.T) {
 	}
 
 	// Turn sc1's connection down.
-	wtb.UpdateSubConnState(sc1, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	scConnErr := errors.New("subConn connection error")
+	wtb.UpdateSubConnState(sc1, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	p = <-cc.NewPickerCh
 	want = []balancer.SubConn{sc4}
 	if err := testutils.IsRoundRobin(want, subConnFromPicker(p)); err != nil {
@@ -586,11 +592,14 @@ func (s) TestWeightedTarget_TwoSubBalancers_MoreBackends(t *testing.T) {
 	}
 
 	// Turn all connections down.
-	wtb.UpdateSubConnState(sc4, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	wtb.UpdateSubConnState(sc4, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	p = <-cc.NewPickerCh
 	for i := 0; i < 5; i++ {
-		if _, err := p.Pick(balancer.PickInfo{}); err != balancer.ErrTransientFailure {
-			t.Fatalf("want pick error %v, got %v", balancer.ErrTransientFailure, err)
+		if _, err := p.Pick(balancer.PickInfo{}); err == nil || !strings.Contains(err.Error(), scConnErr.Error()) {
+			t.Fatalf("want pick error %q, got error %q", scConnErr, err)
 		}
 	}
 }
@@ -793,7 +802,11 @@ func (s) TestWeightedTarget_ThreeSubBalancers_RemoveBalancer(t *testing.T) {
 	}
 
 	// Move balancer 3 into transient failure.
-	wtb.UpdateSubConnState(sc3, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	scConnErr := errors.New("subConn connection error")
+	wtb.UpdateSubConnState(sc3, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	<-cc.NewPickerCh
 
 	// Remove the first balancer, while the third is transient failure.
@@ -827,8 +840,8 @@ func (s) TestWeightedTarget_ThreeSubBalancers_RemoveBalancer(t *testing.T) {
 		t.Fatalf("RemoveSubConn, want %v, got %v", sc1, scRemoved)
 	}
 	for i := 0; i < 5; i++ {
-		if _, err := p.Pick(balancer.PickInfo{}); err != balancer.ErrTransientFailure {
-			t.Fatalf("want pick error %v, got %v", balancer.ErrTransientFailure, err)
+		if _, err := p.Pick(balancer.PickInfo{}); err == nil || !strings.Contains(err.Error(), scConnErr.Error()) {
+			t.Fatalf("want pick error %q, got error %q", scConnErr, err)
 		}
 	}
 }
@@ -1064,15 +1077,21 @@ func (s) TestBalancerGroup_SubBalancerTurnsConnectingFromTransientFailure(t *tes
 
 	// Set both subconn to TransientFailure, this will put both sub-balancers in
 	// transient failure.
-	wtb.UpdateSubConnState(sc1, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	scConnErr := errors.New("subConn connection error")
+	wtb.UpdateSubConnState(sc1, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	<-cc.NewPickerCh
-	wtb.UpdateSubConnState(sc2, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	wtb.UpdateSubConnState(sc2, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	p := <-cc.NewPickerCh
 
 	for i := 0; i < 5; i++ {
-		r, err := p.Pick(balancer.PickInfo{})
-		if err != balancer.ErrTransientFailure {
-			t.Fatalf("want pick to fail with %v, got result %v, err %v", balancer.ErrTransientFailure, r, err)
+		if _, err := p.Pick(balancer.PickInfo{}); err == nil || !strings.Contains(err.Error(), scConnErr.Error()) {
+			t.Fatalf("want pick error %q, got error %q", scConnErr, err)
 		}
 	}
 
@@ -1086,8 +1105,8 @@ func (s) TestBalancerGroup_SubBalancerTurnsConnectingFromTransientFailure(t *tes
 
 	for i := 0; i < 5; i++ {
 		r, err := p.Pick(balancer.PickInfo{})
-		if err != balancer.ErrTransientFailure {
-			t.Fatalf("want pick to fail with %v, got result %v, err %v", balancer.ErrTransientFailure, r, err)
+		if err == nil || !strings.Contains(err.Error(), scConnErr.Error()) {
+			t.Fatalf("want pick error %q, got result %v, err %q", scConnErr, r, err)
 		}
 	}
 }

xds/internal/balancer/clusterresolver/priority_test.go

@@ -19,6 +19,7 @@ package clusterresolver
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"testing"
 	"time"
@@ -247,7 +248,11 @@ func (s) TestEDSPriority_SwitchPriority(t *testing.T) {
 	}
 
 	// Turn down 1, use 2
-	edsb.UpdateSubConnState(sc1, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	scConnErr := errors.New("subConn connection error")
+	edsb.UpdateSubConnState(sc1, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 	addrs2 := <-cc.NewSubConnAddrsCh
 	if got, want := addrs2[0].Addr, testEndpointAddrs[2]; got != want {
 		t.Fatalf("sc is created with addr %v, want %v", got, want)
@@ -274,7 +279,8 @@ func (s) TestEDSPriority_SwitchPriority(t *testing.T) {
 	}
 
 	// Should get an update with 1's old picker, to override 2's old picker.
-	if err := testErrPickerFromCh(cc.NewPickerCh, balancer.ErrTransientFailure); err != nil {
+	want := errors.New("last connection error: subConn connection error")
+	if err := testErrPickerFromCh(cc.NewPickerCh, want); err != nil {
 		t.Fatal(err)
 	}
 
@@ -305,10 +311,15 @@ func (s) TestEDSPriority_HigherDownWhileAddingLower(t *testing.T) {
 	}
 	sc1 := <-cc.NewSubConnCh
 	// Turn down 1, pick should error.
-	edsb.UpdateSubConnState(sc1, balancer.SubConnState{ConnectivityState: connectivity.TransientFailure})
+	scConnErr := errors.New("subConn connection error")
+	edsb.UpdateSubConnState(sc1, balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+		ConnectionError:   scConnErr,
+	})
 
 	// Test pick failure.
-	if err := testErrPickerFromCh(cc.NewPickerCh, balancer.ErrTransientFailure); err != nil {
+	want := errors.New("last connection error: subConn connection error")
+	if err := testErrPickerFromCh(cc.NewPickerCh, want); err != nil {
 		t.Fatal(err)
 	}
 
@@ -463,8 +474,8 @@ func (s) TestEDSPriority_InitTimeout(t *testing.T) {
 
 // Add localities to existing priorities.
 //
-//  - start with 2 locality with p0 and p1
-//  - add localities to existing p0 and p1
+//   - start with 2 locality with p0 and p1
+//   - add localities to existing p0 and p1
 func (s) TestEDSPriority_MultipleLocalities(t *testing.T) {
 	edsb, cc, xdsC, cleanup := setupTestEDS(t, nil)
 	defer cleanup()