Repository: grpc/grpc-go

Issue:
outlierdetection, pickfirst: Remove the balancer attribute to skip ejection using the connectivity state listener
As part of https://github.com/grpc/grpc-go/pull/7908, a workaround was added to make Outlier Detection aware that the health listener is to be used for ejection updates. This workaround should be removed once all petiole policies delegate to pickfirst and ejection happens only using the health listener.

Hints from issue comments:

Solution patch:
diff --git a/balancer/endpointsharding/endpointsharding.go b/balancer/endpointsharding/endpointsharding.go
index 263c024a..9b59bfc1 100644
--- a/balancer/endpointsharding/endpointsharding.go
+++ b/balancer/endpointsharding/endpointsharding.go
@@ -35,11 +35,9 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/base"
-	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/balancer/gracefulswitch"
-	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/serviceconfig"
 )
@@ -48,11 +46,7 @@ import (
 var PickFirstConfig string
 
 func init() {
-	name := pickfirst.Name
-	if !envconfig.NewPickFirstEnabled {
-		name = pickfirstleaf.Name
-	}
-	PickFirstConfig = fmt.Sprintf("[{%q: {}}]", name)
+	PickFirstConfig = fmt.Sprintf("[{%q: {}}]", pickfirstleaf.Name)
 }
 
 // ChildState is the balancer state of a child along with the endpoint which
diff --git a/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go b/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go
index 2fc0a71f..76fa5fea 100644
--- a/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go
+++ b/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go
@@ -54,9 +54,18 @@ func init() {
 	balancer.Register(pickfirstBuilder{})
 }
 
-// enableHealthListenerKeyType is a unique key type used in resolver attributes
-// to indicate whether the health listener usage is enabled.
-type enableHealthListenerKeyType struct{}
+type (
+	// enableHealthListenerKeyType is a unique key type used in resolver
+	// attributes to indicate whether the health listener usage is enabled.
+	enableHealthListenerKeyType struct{}
+	// managedByPickfirstKeyType is an attribute key type to inform Outlier
+	// Detection that the generic health listener is being used.
+	// TODO: https://github.com/grpc/grpc-go/issues/7915 - Remove this when
+	// implementing the dualstack design. This is a hack. Once Dualstack is
+	// completed, outlier detection will stop sending ejection updates through
+	// the connectivity listener.
+	managedByPickfirstKeyType struct{}
+)
 
 var (
 	logger = grpclog.Component("pick-first-leaf-lb")
@@ -140,6 +149,17 @@ func EnableHealthListener(state resolver.State) resolver.State {
 	return state
 }
 
+// IsManagedByPickfirst returns whether an address belongs to a SubConn
+// managed by the pickfirst LB policy.
+// TODO: https://github.com/grpc/grpc-go/issues/7915 - This is a hack to disable
+// outlier_detection via the with connectivity listener when using pick_first.
+// Once Dualstack changes are complete, all SubConns will be created by
+// pick_first and outlier detection will only use the health listener for
+// ejection. This hack can then be removed.
+func IsManagedByPickfirst(addr resolver.Address) bool {
+	return addr.BalancerAttributes.Value(managedByPickfirstKeyType{}) != nil
+}
+
 type pfConfig struct {
 	serviceconfig.LoadBalancingConfig `json:"-"`
 
@@ -166,6 +186,7 @@ type scData struct {
 }
 
 func (b *pickfirstBalancer) newSCData(addr resolver.Address) (*scData, error) {
+	addr.BalancerAttributes = addr.BalancerAttributes.WithValue(managedByPickfirstKeyType{}, true)
 	sd := &scData{
 		rawConnectivityState: connectivity.Idle,
 		effectiveState:       connectivity.Idle,
diff --git a/balancer/weightedroundrobin/balancer.go b/balancer/weightedroundrobin/balancer.go
index c9c5b576..d7b9dc46 100644
--- a/balancer/weightedroundrobin/balancer.go
+++ b/balancer/weightedroundrobin/balancer.go
@@ -29,6 +29,7 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/endpointsharding"
+	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
 	"google.golang.org/grpc/balancer/weightedroundrobin/internal"
 	"google.golang.org/grpc/balancer/weightedtarget"
 	"google.golang.org/grpc/connectivity"
@@ -218,7 +219,9 @@ type wrrBalancer struct {
 }
 
 func (b *wrrBalancer) UpdateClientConnState(ccs balancer.ClientConnState) error {
-	b.logger.Infof("UpdateCCS: %v", ccs)
+	if b.logger.V(2) {
+		b.logger.Infof("UpdateCCS: %v", ccs)
+	}
 	cfg, ok := ccs.BalancerConfig.(*lbConfig)
 	if !ok {
 		return fmt.Errorf("wrr: received nil or illegal BalancerConfig (type %T): %v", ccs.BalancerConfig, ccs.BalancerConfig)
@@ -232,6 +235,9 @@ func (b *wrrBalancer) UpdateClientConnState(ccs balancer.ClientConnState) error
 	b.updateEndpointsLocked(ccs.ResolverState.Endpoints)
 	b.mu.Unlock()
 
+	// Make pickfirst children use health listeners for outlier detection to
+	// work.
+	ccs.ResolverState = pickfirstleaf.EnableHealthListener(ccs.ResolverState)
 	// This causes child to update picker inline and will thus cause inline
 	// picker update.
 	return b.child.UpdateClientConnState(balancer.ClientConnState{
diff --git a/internal/envconfig/envconfig.go b/internal/envconfig/envconfig.go
index 6e7dd6b7..1e42b6fd 100644
--- a/internal/envconfig/envconfig.go
+++ b/internal/envconfig/envconfig.go
@@ -49,7 +49,7 @@ var (
 	// XDSFallbackSupport is the env variable that controls whether support for
 	// xDS fallback is turned on. If this is unset or is false, only the first
 	// xDS server in the list of server configs will be used.
-	XDSFallbackSupport = boolFromEnv("GRPC_EXPERIMENTAL_XDS_FALLBACK", false)
+	XDSFallbackSupport = boolFromEnv("GRPC_EXPERIMENTAL_XDS_FALLBACK", true)
 	// NewPickFirstEnabled is set if the new pickfirst leaf policy is to be used
 	// instead of the exiting pickfirst implementation. This can be enabled by
 	// setting the environment variable "GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST"
diff --git a/xds/internal/balancer/outlierdetection/balancer.go b/xds/internal/balancer/outlierdetection/balancer.go
index c9d496ce..8f58c003 100644
--- a/xds/internal/balancer/outlierdetection/balancer.go
+++ b/xds/internal/balancer/outlierdetection/balancer.go
@@ -33,6 +33,7 @@ import (
 	"unsafe"
 
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/balancer/gracefulswitch"
 	"google.golang.org/grpc/internal/buffer"
@@ -72,7 +73,7 @@ func (bb) Build(cc balancer.ClientConn, bOpts balancer.BuildOptions) balancer.Ba
 	}
 	b.logger = prefixLogger(b)
 	b.logger.Infof("Created")
-	b.child = gracefulswitch.NewBalancer(b, bOpts)
+	b.child = synchronizingBalancerWrapper{lb: gracefulswitch.NewBalancer(b, bOpts)}
 	go b.run()
 	return b
 }
@@ -152,6 +153,11 @@ type lbCfgUpdate struct {
 	done chan struct{}
 }
 
+type scHealthUpdate struct {
+	scw   *subConnWrapper
+	state balancer.SubConnState
+}
+
 type outlierDetectionBalancer struct {
 	// These fields are safe to be accessed without holding any mutex because
 	// they are synchronized in run(), which makes these field accesses happen
@@ -170,10 +176,7 @@ type outlierDetectionBalancer struct {
 	logger         *grpclog.PrefixLogger
 	channelzParent channelz.Identifier
 
-	// childMu guards calls into child (to uphold the balancer.Balancer API
-	// guarantee of synchronous calls).
-	childMu sync.Mutex
-	child   *gracefulswitch.Balancer
+	child synchronizingBalancerWrapper
 
 	// mu guards access to the following fields. It also helps to synchronize
 	// behaviors of the following events: config updates, firing of the interval
@@ -190,8 +193,8 @@ type outlierDetectionBalancer struct {
 	// which uses addrs. This balancer waits for the interval timer algorithm to
 	// finish before making the update to the addrs map.
 	//
-	// This mutex is never held at the same time as childMu (within the context
-	// of a single goroutine).
+	// This mutex is never held when calling methods on the child policy
+	// (within the context of a single goroutine).
 	mu                    sync.Mutex
 	addrs                 map[string]*addressInfo
 	cfg                   *LBConfig
@@ -276,13 +279,9 @@ func (b *outlierDetectionBalancer) UpdateClientConnState(s balancer.ClientConnSt
 	// the balancer.Balancer API, so it is guaranteed to be called in a
 	// synchronous manner, so it cannot race with this read.
 	if b.cfg == nil || b.cfg.ChildPolicy.Name != lbCfg.ChildPolicy.Name {
-		b.childMu.Lock()
-		err := b.child.SwitchTo(bb)
-		if err != nil {
-			b.childMu.Unlock()
+		if err := b.child.switchTo(bb); err != nil {
 			return fmt.Errorf("outlier detection: error switching to child of type %q: %v", lbCfg.ChildPolicy.Name, err)
 		}
-		b.childMu.Unlock()
 	}
 
 	b.mu.Lock()
@@ -319,12 +318,10 @@ func (b *outlierDetectionBalancer) UpdateClientConnState(s balancer.ClientConnSt
 	}
 	b.mu.Unlock()
 
-	b.childMu.Lock()
-	err := b.child.UpdateClientConnState(balancer.ClientConnState{
+	err := b.child.updateClientConnState(balancer.ClientConnState{
 		ResolverState:  s.ResolverState,
 		BalancerConfig: b.cfg.ChildPolicy.Config,
 	})
-	b.childMu.Unlock()
 
 	done := make(chan struct{})
 	b.pickerUpdateCh.Put(lbCfgUpdate{
@@ -337,9 +334,7 @@ func (b *outlierDetectionBalancer) UpdateClientConnState(s balancer.ClientConnSt
 }
 
 func (b *outlierDetectionBalancer) ResolverError(err error) {
-	b.childMu.Lock()
-	defer b.childMu.Unlock()
-	b.child.ResolverError(err)
+	b.child.resolverError(err)
 }
 
 func (b *outlierDetectionBalancer) updateSubConnState(sc balancer.SubConn, state balancer.SubConnState) {
@@ -355,6 +350,7 @@ func (b *outlierDetectionBalancer) updateSubConnState(sc balancer.SubConn, state
 	if state.ConnectivityState == connectivity.Shutdown {
 		delete(b.scWrappers, scw.SubConn)
 	}
+	scw.setLatestConnectivityState(state.ConnectivityState)
 	b.scUpdateCh.Put(&scUpdate{
 		scw:   scw,
 		state: state,
@@ -368,9 +364,7 @@ func (b *outlierDetectionBalancer) UpdateSubConnState(sc balancer.SubConn, state
 func (b *outlierDetectionBalancer) Close() {
 	b.closed.Fire()
 	<-b.done.Done()
-	b.childMu.Lock()
-	b.child.Close()
-	b.childMu.Unlock()
+	b.child.closeLB()
 
 	b.scUpdateCh.Close()
 	b.pickerUpdateCh.Close()
@@ -383,9 +377,7 @@ func (b *outlierDetectionBalancer) Close() {
 }
 
 func (b *outlierDetectionBalancer) ExitIdle() {
-	b.childMu.Lock()
-	defer b.childMu.Unlock()
-	b.child.ExitIdle()
+	b.child.exitIdle()
 }
 
 // wrappedPicker delegates to the child policy's picker, and when the request
@@ -475,10 +467,13 @@ func (b *outlierDetectionBalancer) NewSubConn(addrs []resolver.Address, opts bal
 		return nil, err
 	}
 	scw := &subConnWrapper{
-		SubConn:    sc,
-		addresses:  addrs,
-		scUpdateCh: b.scUpdateCh,
-		listener:   oldListener,
+		SubConn:                    sc,
+		addresses:                  addrs,
+		scUpdateCh:                 b.scUpdateCh,
+		listener:                   oldListener,
+		latestRawConnectivityState: balancer.SubConnState{ConnectivityState: connectivity.Idle},
+		latestHealthState:          balancer.SubConnState{ConnectivityState: connectivity.Connecting},
+		healthListenerEnabled:      len(addrs) == 1 && pickfirstleaf.IsManagedByPickfirst(addrs[0]),
 	}
 	b.mu.Lock()
 	defer b.mu.Unlock()
@@ -596,34 +591,18 @@ func (b *outlierDetectionBalancer) Target() string {
 // if the SubConn is not ejected.
 func (b *outlierDetectionBalancer) handleSubConnUpdate(u *scUpdate) {
 	scw := u.scw
-	scw.latestState = u.state
-	if !scw.ejected {
-		if scw.listener != nil {
-			b.childMu.Lock()
-			scw.listener(u.state)
-			b.childMu.Unlock()
-		}
-	}
+	scw.clearHealthListener()
+	b.child.updateSubConnState(scw, u.state)
+}
+
+func (b *outlierDetectionBalancer) handleSubConnHealthUpdate(u *scHealthUpdate) {
+	b.child.updateSubConnHealthState(u.scw, u.state)
 }
 
 // handleEjectedUpdate handles any SubConns that get ejected/unejected, and
 // forwards the appropriate corresponding subConnState to the child policy.
 func (b *outlierDetectionBalancer) handleEjectedUpdate(u *ejectionUpdate) {
-	scw := u.scw
-	scw.ejected = u.isEjected
-	// If scw.latestState has never been written to will default to connectivity
-	// IDLE, which is fine.
-	stateToUpdate := scw.latestState
-	if u.isEjected {
-		stateToUpdate = balancer.SubConnState{
-			ConnectivityState: connectivity.TransientFailure,
-		}
-	}
-	if scw.listener != nil {
-		b.childMu.Lock()
-		scw.listener(stateToUpdate)
-		b.childMu.Unlock()
-	}
+	b.child.handleEjectionUpdate(u)
 }
 
 // handleChildStateUpdate forwards the picker update wrapped in a wrapped picker
@@ -696,6 +675,8 @@ func (b *outlierDetectionBalancer) run() {
 				b.handleSubConnUpdate(u)
 			case *ejectionUpdate:
 				b.handleEjectedUpdate(u)
+			case *scHealthUpdate:
+				b.handleSubConnHealthUpdate(u)
 			}
 		case update, ok := <-b.pickerUpdateCh.Get():
 			if !ok {
@@ -880,6 +861,69 @@ func (b *outlierDetectionBalancer) unejectAddress(addrInfo *addressInfo) {
 	}
 }
 
+// synchronizingBalancerWrapper serializes calls into balancer (to uphold the
+// balancer.Balancer API guarantee of synchronous calls). It also ensures a
+// consistent order of locking mutexes when using SubConn listeners to avoid
+// deadlocks.
+type synchronizingBalancerWrapper struct {
+	// mu should not be used directly from outside this struct, instead use
+	// methods defined on the struct.
+	mu sync.Mutex
+	lb *gracefulswitch.Balancer
+}
+
+func (sbw *synchronizingBalancerWrapper) switchTo(builder balancer.Builder) error {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	return sbw.lb.SwitchTo(builder)
+}
+
+func (sbw *synchronizingBalancerWrapper) updateClientConnState(state balancer.ClientConnState) error {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	return sbw.lb.UpdateClientConnState(state)
+}
+
+func (sbw *synchronizingBalancerWrapper) resolverError(err error) {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	sbw.lb.ResolverError(err)
+}
+
+func (sbw *synchronizingBalancerWrapper) closeLB() {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	sbw.lb.Close()
+}
+
+func (sbw *synchronizingBalancerWrapper) exitIdle() {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	sbw.lb.ExitIdle()
+}
+
+func (sbw *synchronizingBalancerWrapper) updateSubConnHealthState(scw *subConnWrapper, scs balancer.SubConnState) {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	scw.updateSubConnHealthState(scs)
+}
+
+func (sbw *synchronizingBalancerWrapper) updateSubConnState(scw *subConnWrapper, scs balancer.SubConnState) {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	scw.updateSubConnConnectivityState(scs)
+}
+
+func (sbw *synchronizingBalancerWrapper) handleEjectionUpdate(u *ejectionUpdate) {
+	sbw.mu.Lock()
+	defer sbw.mu.Unlock()
+	if u.isEjected {
+		u.scw.handleEjection()
+	} else {
+		u.scw.handleUnejection()
+	}
+}
+
 // addressInfo contains the runtime information about an address that pertains
 // to Outlier Detection. This struct and all of its fields is protected by
 // outlierDetectionBalancer.mu in the case where it is accessed through the
diff --git a/xds/internal/balancer/outlierdetection/subconn_wrapper.go b/xds/internal/balancer/outlierdetection/subconn_wrapper.go
index 0fa422d8..7d710fde 100644
--- a/xds/internal/balancer/outlierdetection/subconn_wrapper.go
+++ b/xds/internal/balancer/outlierdetection/subconn_wrapper.go
@@ -19,9 +19,11 @@ package outlierdetection
 
 import (
 	"fmt"
+	"sync"
 	"unsafe"
 
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/buffer"
 	"google.golang.org/grpc/resolver"
 )
@@ -31,23 +33,54 @@ import (
 // whether or not this SubConn is ejected.
 type subConnWrapper struct {
 	balancer.SubConn
-	listener func(balancer.SubConnState)
-
 	// addressInfo is a pointer to the subConnWrapper's corresponding address
-	// map entry, if the map entry exists.
+	// map entry, if the map entry exists. It is accessed atomically.
 	addressInfo unsafe.Pointer // *addressInfo
+	// The following fields are set during object creation and read-only after
+	// that.
+
+	listener func(balancer.SubConnState)
+	// healthListenerEnabled indicates whether the leaf LB policy is using a
+	// generic health listener. When enabled, ejection updates are sent via the
+	// health listener instead of the connectivity listener. Once Dualstack
+	// changes are complete, all SubConns will be created by pickfirst which
+	// uses the health listener.
+	// TODO: https://github.com/grpc/grpc-go/issues/7915 - Once Dualstack
+	// changes are complete, all SubConns will be created by pick_first and
+	// outlier detection will only use the health listener for ejection and
+	// this field can be removed.
+	healthListenerEnabled bool
+
+	scUpdateCh *buffer.Unbounded
+
+	// The following fields are only referenced in the context of a work
+	// serializing buffer and don't need to be protected by a mutex.
+
 	// These two pieces of state will reach eventual consistency due to sync in
 	// run(), and child will always have the correctly updated SubConnState.
-	// latestState is the latest state update from the underlying SubConn. This
-	// is used whenever a SubConn gets unejected.
-	latestState balancer.SubConnState
-	ejected     bool
 
-	scUpdateCh *buffer.Unbounded
+	ejected bool
 
 	// addresses is the list of address(es) this SubConn was created with to
 	// help support any change in address(es)
 	addresses []resolver.Address
+	// latestHealthState is tracked to update the child policy during
+	// unejection.
+	latestHealthState balancer.SubConnState
+	// latestRawConnectivityState is tracked to update the child policy during
+	// unejection.
+	latestRawConnectivityState balancer.SubConnState
+
+	// Access to the following fields are protected by a mutex. These fields
+	// should not be accessed from outside this file, instead use methods
+	// defined on the struct.
+	mu             sync.Mutex
+	healthListener func(balancer.SubConnState)
+	// latestReceivedConnectivityState is the SubConn's most recent connectivity
+	// state received. It may not be delivered to the child balancer yet. It is
+	// used to ensure a health listener is registered with the SubConn only when
+	// the SubConn is READY.
+	latestReceivedConnectivityState connectivity.State
 }
 
 // eject causes the wrapper to report a state update with the TRANSIENT_FAILURE
@@ -72,3 +105,108 @@ func (scw *subConnWrapper) uneject() {
 func (scw *subConnWrapper) String() string {
 	return fmt.Sprintf("%+v", scw.addresses)
 }
+
+func (scw *subConnWrapper) RegisterHealthListener(listener func(balancer.SubConnState)) {
+	// gRPC currently supports two mechanisms that provide a health signal for
+	// a connection: client-side health checking and outlier detection. Earlier
+	// both these mechanisms signaled unhealthiness by setting the subchannel
+	// state to TRANSIENT_FAILURE. As part of the dualstack changes to make
+	// pick_first the universal leaf policy (see A61), both these mechanisms
+	// started using the new health listener to make health signal visible to
+	// the petiole policies without affecting the underlying connectivity
+	// management of the pick_first policy
+	if !scw.healthListenerEnabled {
+		logger.Errorf("Health listener unexpectedly registered on SubConn %v.", scw)
+		return
+	}
+
+	scw.mu.Lock()
+	defer scw.mu.Unlock()
+
+	if scw.latestReceivedConnectivityState != connectivity.Ready {
+		return
+	}
+	scw.healthListener = listener
+	if listener == nil {
+		scw.SubConn.RegisterHealthListener(nil)
+		return
+	}
+
+	scw.SubConn.RegisterHealthListener(func(scs balancer.SubConnState) {
+		scw.scUpdateCh.Put(&scHealthUpdate{
+			scw:   scw,
+			state: scs,
+		})
+	})
+}
+
+// updateSubConnHealthState stores the latest health state for unejection and
+// sends updates the health listener.
+func (scw *subConnWrapper) updateSubConnHealthState(scs balancer.SubConnState) {
+	scw.latestHealthState = scs
+	if scw.ejected {
+		return
+	}
+	scw.mu.Lock()
+	defer scw.mu.Unlock()
+	if scw.healthListener != nil {
+		scw.healthListener(scs)
+	}
+}
+
+// updateSubConnConnectivityState stores the latest connectivity state for
+// unejection and updates the raw connectivity listener.
+func (scw *subConnWrapper) updateSubConnConnectivityState(scs balancer.SubConnState) {
+	scw.latestRawConnectivityState = scs
+	// If the raw connectivity listener is used for ejection, and the SubConn is
+	// ejected, don't send the update.
+	if scw.ejected && !scw.healthListenerEnabled {
+		return
+	}
+	if scw.listener != nil {
+		scw.listener(scs)
+	}
+}
+
+func (scw *subConnWrapper) clearHealthListener() {
+	scw.mu.Lock()
+	defer scw.mu.Unlock()
+	scw.healthListener = nil
+}
+
+func (scw *subConnWrapper) handleUnejection() {
+	scw.ejected = false
+	if !scw.healthListenerEnabled {
+		// If scw.latestRawConnectivityState has never been written to will
+		// default to connectivity IDLE, which is fine.
+		scw.updateSubConnConnectivityState(scw.latestRawConnectivityState)
+		return
+	}
+	// If scw.latestHealthState has never been written to will use the health
+	// state CONNECTING set during object creation.
+	scw.updateSubConnHealthState(scw.latestHealthState)
+}
+
+func (scw *subConnWrapper) handleEjection() {
+	scw.ejected = true
+	stateToUpdate := balancer.SubConnState{
+		ConnectivityState: connectivity.TransientFailure,
+	}
+	if !scw.healthListenerEnabled {
+		if scw.listener != nil {
+			scw.listener(stateToUpdate)
+		}
+		return
+	}
+	scw.mu.Lock()
+	defer scw.mu.Unlock()
+	if scw.healthListener != nil {
+		scw.healthListener(stateToUpdate)
+	}
+}
+
+func (scw *subConnWrapper) setLatestConnectivityState(state connectivity.State) {
+	scw.mu.Lock()
+	defer scw.mu.Unlock()
+	scw.latestReceivedConnectivityState = state
+}



Test patch:
diff --git a/balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go b/balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go
index 9667c2b3..2a87d669 100644
--- a/balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go
+++ b/balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go
@@ -58,7 +58,13 @@ const (
 	stateStoringBalancerName = "state_storing"
 )
 
-var stateStoringServiceConfig = fmt.Sprintf(`{"loadBalancingConfig": [{"%s":{}}]}`, stateStoringBalancerName)
+var (
+	stateStoringServiceConfig = fmt.Sprintf(`{"loadBalancingConfig": [{"%s":{}}]}`, stateStoringBalancerName)
+	ignoreBalAttributesOpt    = cmp.Transformer("IgnoreBalancerAttributes", func(a resolver.Address) resolver.Address {
+		a.BalancerAttributes = nil
+		return a
+	})
+)
 
 type s struct {
 	grpctest.Tester
@@ -177,7 +183,7 @@ func (s) TestPickFirstLeaf_SimpleResolverUpdate_FirstServerReady(t *testing.T) {
 	wantSCStates := []scState{
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Ready},
 	}
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -219,7 +225,7 @@ func (s) TestPickFirstLeaf_SimpleResolverUpdate_FirstServerUnReady(t *testing.T)
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Shutdown},
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -264,7 +270,7 @@ func (s) TestPickFirstLeaf_SimpleResolverUpdate_DuplicateAddrs(t *testing.T) {
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Shutdown},
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -317,7 +323,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_DisjointLists(t *testing.T) {
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -334,7 +340,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_DisjointLists(t *testing.T) {
 		{Addrs: []resolver.Address{addrs[3]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -378,7 +384,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_ActiveBackendInUpdatedList(t *testing
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -398,7 +404,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_ActiveBackendInUpdatedList(t *testing
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -440,7 +446,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_InActiveBackendInUpdatedList(t *testi
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -458,7 +464,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_InActiveBackendInUpdatedList(t *testi
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -502,7 +508,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_IdenticalLists(t *testing.T) {
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -521,7 +527,7 @@ func (s) TestPickFirstLeaf_ResolverUpdates_IdenticalLists(t *testing.T) {
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -576,7 +582,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_FirstServerRestart(t *testing.T)
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -591,7 +597,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_FirstServerRestart(t *testing.T)
 		t.Fatal(err)
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -639,7 +645,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_SecondServerRestart(t *testing.T)
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -660,7 +666,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_SecondServerRestart(t *testing.T)
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Shutdown},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -708,7 +714,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_SecondServerToFirst(t *testing.T)
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -729,7 +735,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_SecondServerToFirst(t *testing.T)
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -776,7 +782,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_FirstServerToSecond(t *testing.T)
 		{Addrs: []resolver.Address{addrs[0]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -796,7 +802,7 @@ func (s) TestPickFirstLeaf_StopConnectedServer_FirstServerToSecond(t *testing.T)
 		{Addrs: []resolver.Address{addrs[1]}, State: connectivity.Ready},
 	}
 
-	if diff := cmp.Diff(wantSCStates, bal.subConnStates()); diff != "" {
+	if diff := cmp.Diff(wantSCStates, bal.subConnStates(), ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn states mismatch (-want +got):\n%s", diff)
 	}
 
@@ -1130,7 +1136,7 @@ func (s) TestPickFirstLeaf_InterleavingIPV4Preffered(t *testing.T) {
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
-	if diff := cmp.Diff(wantAddrs, gotAddrs); diff != "" {
+	if diff := cmp.Diff(wantAddrs, gotAddrs, ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn creation order mismatch (-want +got):\n%s", diff)
 	}
 }
@@ -1174,7 +1180,7 @@ func (s) TestPickFirstLeaf_InterleavingIPv6Preffered(t *testing.T) {
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
-	if diff := cmp.Diff(wantAddrs, gotAddrs); diff != "" {
+	if diff := cmp.Diff(wantAddrs, gotAddrs, ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn creation order mismatch (-want +got):\n%s", diff)
 	}
 }
@@ -1220,7 +1226,7 @@ func (s) TestPickFirstLeaf_InterleavingUnknownPreffered(t *testing.T) {
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
-	if diff := cmp.Diff(wantAddrs, gotAddrs); diff != "" {
+	if diff := cmp.Diff(wantAddrs, gotAddrs, ignoreBalAttributesOpt); diff != "" {
 		t.Errorf("SubConn creation order mismatch (-want +got):\n%s", diff)
 	}
 }
diff --git a/internal/xds/bootstrap/bootstrap_test.go b/internal/xds/bootstrap/bootstrap_test.go
index 302e2814..d0571978 100644
--- a/internal/xds/bootstrap/bootstrap_test.go
+++ b/internal/xds/bootstrap/bootstrap_test.go
@@ -429,10 +429,6 @@ func (s) TestGetConfiguration_Success(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			origFallbackEnv := envconfig.XDSFallbackSupport
-			envconfig.XDSFallbackSupport = true
-			defer func() { envconfig.XDSFallbackSupport = origFallbackEnv }()
-
 			testGetConfigurationWithFileNameEnv(t, test.name, false, test.wantConfig)
 			testGetConfigurationWithFileContentEnv(t, test.name, false, test.wantConfig)
 		})
@@ -1202,9 +1198,9 @@ func (s) TestNode_ToProto(t *testing.T) {
 // Tests the case where the xDS fallback env var is set to false, and verifies
 // that only the first server from the list of server configurations is used.
 func (s) TestGetConfiguration_FallbackDisabled(t *testing.T) {
-	// TODO(easwars): Default value of "GRPC_EXPERIMENTAL_XDS_FALLBACK"
-	// env var is currently false. When the default is changed to true,
-	// explicitly set it to false here.
+	origFallbackEnv := envconfig.XDSFallbackSupport
+	envconfig.XDSFallbackSupport = false
+	defer func() { envconfig.XDSFallbackSupport = origFallbackEnv }()
 
 	cancel := setupBootstrapOverride(map[string]string{
 		"multipleXDSServers": `
diff --git a/test/compressor_test.go b/test/compressor_test.go
index 0495a06f..0a629bce 100644
--- a/test/compressor_test.go
+++ b/test/compressor_test.go
@@ -785,3 +785,62 @@ func (s) TestGzipBadChecksum(t *testing.T) {
 		t.Errorf("ss.Client.UnaryCall(_) = _, %v\n\twant: _, status(codes.Internal, contains %q)", err, gzip.ErrChecksum)
 	}
 }
+
+// fakeCompressor returns a messages of a configured size, irrespective of the
+// input.
+type fakeCompressor struct {
+	decompressedMessageSize int
+}
+
+func (f *fakeCompressor) Compress(w io.Writer) (io.WriteCloser, error) {
+	return nopWriteCloser{w}, nil
+}
+
+func (f *fakeCompressor) Decompress(io.Reader) (io.Reader, error) {
+	return bytes.NewReader(make([]byte, f.decompressedMessageSize)), nil
+}
+
+func (f *fakeCompressor) Name() string {
+	// Use the name of an existing compressor to avoid interactions with other
+	// tests since compressors can't be un-registered.
+	return "gzip"
+}
+
+type nopWriteCloser struct {
+	io.Writer
+}
+
+func (nopWriteCloser) Close() error {
+	return nil
+}
+
+// TestDecompressionExceedsMaxMessageSize uses a fake compressor that produces
+// messages of size 100 bytes on decompression. A server is started with the
+// max receive message size restricted to 99 bytes. The test verifies that the
+// client receives a ResourceExhausted response from the server.
+func (s) TestDecompressionExceedsMaxMessageSize(t *testing.T) {
+	oldC := encoding.GetCompressor("gzip")
+	defer func() {
+		encoding.RegisterCompressor(oldC)
+	}()
+	const messageLen = 100
+	encoding.RegisterCompressor(&fakeCompressor{decompressedMessageSize: messageLen})
+	ss := &stubserver.StubServer{
+		UnaryCallF: func(context.Context, *testpb.SimpleRequest) (*testpb.SimpleResponse, error) {
+			return &testpb.SimpleResponse{}, nil
+		},
+	}
+	if err := ss.Start([]grpc.ServerOption{grpc.MaxRecvMsgSize(messageLen - 1)}); err != nil {
+		t.Fatalf("Error starting endpoint server: %v", err)
+	}
+	defer ss.Stop()
+
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+
+	req := &testpb.SimpleRequest{Payload: &testpb.Payload{}}
+	_, err := ss.Client.UnaryCall(ctx, req, grpc.UseCompressor("gzip"))
+	if got, want := status.Code(err), codes.ResourceExhausted; got != want {
+		t.Errorf("Client.UnaryCall(%+v) returned status %v, want %v", req, got, want)
+	}
+}
diff --git a/test/creds_test.go b/test/creds_test.go
index c9b88624..fe8b552e 100644
--- a/test/creds_test.go
+++ b/test/creds_test.go
@@ -243,15 +243,8 @@ func (s) TestFailFastRPCErrorOnBadCertificates(t *testing.T) {
 	defer cc.Close()
 
 	tc := testgrpc.NewTestServiceClient(cc)
-	for i := 0; i < 1000; i++ {
-		// This loop runs for at most 1 second. The first several RPCs will fail
-		// with Unavailable because the connection hasn't started. When the
-		// first connection failed with creds error, the next RPC should also
-		// fail with the expected error.
-		if _, err = tc.EmptyCall(ctx, &testpb.Empty{}); strings.Contains(err.Error(), clientAlwaysFailCredErrorMsg) {
-			return
-		}
-		time.Sleep(time.Millisecond)
+	if _, err = tc.EmptyCall(ctx, &testpb.Empty{}); strings.Contains(err.Error(), clientAlwaysFailCredErrorMsg) {
+		return
 	}
 	te.t.Fatalf("TestService/EmptyCall(_, _) = _, %v, want err.Error() contains %q", err, clientAlwaysFailCredErrorMsg)
 }
@@ -268,8 +261,18 @@ func (s) TestWaitForReadyRPCErrorOnBadCertificates(t *testing.T) {
 	}
 	defer cc.Close()
 
+	// The DNS resolver may take more than defaultTestShortTimeout, we let the
+	// channel enter TransientFailure signalling that the first resolver state
+	// has been produced.
+	cc.Connect()
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+	testutils.AwaitState(ctx, t, cc, connectivity.TransientFailure)
+
 	tc := testgrpc.NewTestServiceClient(cc)
-	ctx, cancel := context.WithTimeout(context.Background(), defaultTestShortTimeout)
+	// Use a short context as WaitForReady waits for context expiration before
+	// failing the RPC.
+	ctx, cancel = context.WithTimeout(context.Background(), defaultTestShortTimeout)
 	defer cancel()
 	if _, err = tc.EmptyCall(ctx, &testpb.Empty{}, grpc.WaitForReady(true)); !strings.Contains(err.Error(), clientAlwaysFailCredErrorMsg) {
 		t.Fatalf("TestService/EmptyCall(_, _) = _, %v, want err.Error() contains %q", err, clientAlwaysFailCredErrorMsg)
diff --git a/xds/internal/balancer/outlierdetection/balancer_test.go b/xds/internal/balancer/outlierdetection/balancer_test.go
index a80d4d9d..ca07dcda 100644
--- a/xds/internal/balancer/outlierdetection/balancer_test.go
+++ b/xds/internal/balancer/outlierdetection/balancer_test.go
@@ -31,17 +31,24 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
+	"google.golang.org/grpc"
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
 	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal/balancer/stub"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/internal/grpctest"
 	iserviceconfig "google.golang.org/grpc/internal/serviceconfig"
+	"google.golang.org/grpc/internal/stubserver"
 	"google.golang.org/grpc/internal/testutils"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/serviceconfig"
 	"google.golang.org/grpc/xds/internal/balancer/clusterimpl"
+
+	testgrpc "google.golang.org/grpc/interop/grpc_testing"
+	testpb "google.golang.org/grpc/interop/grpc_testing"
 )
 
 var (
@@ -1568,3 +1575,92 @@ func (s) TestConcurrentOperations(t *testing.T) {
 	close(finished)
 	wg.Wait()
 }
+
+// Test verifies that outlier detection doesn't eject subchannels created by
+// the new pickfirst balancer when pickfirst is a non-leaf policy, i.e. not
+// under a petiole policy. When pickfirst is not under a petiole policy, it will
+// not register a health listener. pickfirst will still set the address
+// attribute to disable ejection through the raw connectivity listener. When
+// Outlier Detection processes a health update and sees the health listener is
+// enabled but a health listener is not registered, it will drop the ejection
+// update.
+func (s) TestPickFirstHealthListenerDisabled(t *testing.T) {
+	backend := &stubserver.StubServer{
+		EmptyCallF: func(context.Context, *testpb.Empty) (*testpb.Empty, error) {
+			return nil, errors.New("some error")
+		},
+	}
+	if err := backend.StartServer(); err != nil {
+		t.Fatalf("Failed to start backend: %v", err)
+	}
+	defer backend.Stop()
+	t.Logf("Started bad TestService backend at: %q", backend.Address)
+
+	// The interval is intentionally kept very large, the interval algorithm
+	// will be triggered manually.
+	odCfg := &LBConfig{
+		Interval:         iserviceconfig.Duration(300 * time.Second),
+		BaseEjectionTime: iserviceconfig.Duration(300 * time.Second),
+		MaxEjectionTime:  iserviceconfig.Duration(500 * time.Second),
+		FailurePercentageEjection: &FailurePercentageEjection{
+			Threshold:             50,
+			EnforcementPercentage: 100,
+			MinimumHosts:          0,
+			RequestVolume:         2,
+		},
+		MaxEjectionPercent: 100,
+		ChildPolicy: &iserviceconfig.BalancerConfig{
+			Name: pickfirstleaf.Name,
+		},
+	}
+
+	lbChan := make(chan *outlierDetectionBalancer, 1)
+	bf := stub.BalancerFuncs{
+		Init: func(bd *stub.BalancerData) {
+			bd.Data = balancer.Get(Name).Build(bd.ClientConn, bd.BuildOptions)
+			lbChan <- bd.Data.(*outlierDetectionBalancer)
+		},
+		Close: func(bd *stub.BalancerData) {
+			bd.Data.(balancer.Balancer).Close()
+		},
+		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
+			ccs.BalancerConfig = odCfg
+			return bd.Data.(balancer.Balancer).UpdateClientConnState(ccs)
+		},
+	}
+
+	stub.Register(t.Name(), bf)
+
+	opts := []grpc.DialOption{
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithDefaultServiceConfig(fmt.Sprintf(`{ "loadBalancingConfig": [{%q: {}}] }`, t.Name())),
+	}
+	cc, err := grpc.NewClient(backend.Address, opts...)
+	if err != nil {
+		t.Fatalf("grpc.NewClient() failed: %v", err)
+	}
+	defer cc.Close()
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+	testServiceClient := testgrpc.NewTestServiceClient(cc)
+	testServiceClient.EmptyCall(ctx, &testpb.Empty{})
+	testutils.AwaitState(ctx, t, cc, connectivity.Ready)
+
+	// Failing request should not cause ejection.
+	testServiceClient.EmptyCall(ctx, &testpb.Empty{})
+	testServiceClient.EmptyCall(ctx, &testpb.Empty{})
+	testServiceClient.EmptyCall(ctx, &testpb.Empty{})
+	testServiceClient.EmptyCall(ctx, &testpb.Empty{})
+
+	// Run the interval algorithm.
+	select {
+	case <-ctx.Done():
+		t.Fatal("Timed out waiting for the outlier detection LB policy to be built.")
+	case od := <-lbChan:
+		od.intervalTimerAlgorithm()
+	}
+
+	shortCtx, shortCancel := context.WithTimeout(ctx, defaultTestShortTimeout)
+	defer shortCancel()
+	testutils.AwaitNoStateChange(shortCtx, t, cc, connectivity.Ready)
+}
diff --git a/xds/internal/balancer/outlierdetection/e2e_test/outlierdetection_test.go b/xds/internal/balancer/outlierdetection/e2e_test/outlierdetection_test.go
index 35c4d753..ec087eb0 100644
--- a/xds/internal/balancer/outlierdetection/e2e_test/outlierdetection_test.go
+++ b/xds/internal/balancer/outlierdetection/e2e_test/outlierdetection_test.go
@@ -28,8 +28,10 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/balancer/weightedroundrobin"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/stubserver"
 	"google.golang.org/grpc/peer"
@@ -43,7 +45,18 @@ import (
 	_ "google.golang.org/grpc/xds/internal/balancer/outlierdetection" // To register helper functions which register/unregister Outlier Detection LB Policy.
 )
 
-var defaultTestTimeout = 5 * time.Second
+var (
+	defaultTestTimeout = 5 * time.Second
+	leafPolicyName     = "round_robin"
+)
+
+func init() {
+	// Test the health listener code path for ejection when the experimental
+	// pickfirst is enabled.
+	if envconfig.NewPickFirstEnabled {
+		leafPolicyName = weightedroundrobin.Name
+	}
+}
 
 type s struct {
 	grpctest.Tester
@@ -155,50 +168,50 @@ func (s) TestOutlierDetectionAlgorithmsE2E(t *testing.T) {
 	}{
 		{
 			name: "Success Rate Algorithm",
-			odscJSON: `
-{
-  "loadBalancingConfig": [
-    {
-      "outlier_detection_experimental": {
-        "interval": "0.050s",
-		"baseEjectionTime": "0.100s",
-		"maxEjectionTime": "300s",
-		"maxEjectionPercent": 33,
-		"successRateEjection": {
-			"stdevFactor": 50,
-			"enforcementPercentage": 100,
-			"minimumHosts": 3,
-			"requestVolume": 5
-		},
-        "childPolicy": [{"round_robin": {}}]
-      }
-    }
-  ]
-}`,
+			odscJSON: fmt.Sprintf(`
+			{
+			  "loadBalancingConfig": [
+				{
+				  "outlier_detection_experimental": {
+					"interval": "0.050s",
+					"baseEjectionTime": "0.100s",
+					"maxEjectionTime": "300s",
+					"maxEjectionPercent": 33,
+					"successRateEjection": {
+						"stdevFactor": 50,
+						"enforcementPercentage": 100,
+						"minimumHosts": 3,
+						"requestVolume": 5
+					},
+					"childPolicy": [{"%s": {}}]
+				  }
+				}
+			  ]
+			}`, leafPolicyName),
 		},
 		{
 			name: "Failure Percentage Algorithm",
-			odscJSON: `
-{
-  "loadBalancingConfig": [
-    {
-      "outlier_detection_experimental": {
-        "interval": "0.050s",
-		"baseEjectionTime": "0.100s",
-		"maxEjectionTime": "300s",
-		"maxEjectionPercent": 33,
-		"failurePercentageEjection": {
-			"threshold": 50,
-			"enforcementPercentage": 100,
-			"minimumHosts": 3,
-			"requestVolume": 5
-		},
-        "childPolicy": [{"round_robin": {}}
-		]
-      }
-    }
-  ]
-}`,
+			odscJSON: fmt.Sprintf(`
+			{
+			  "loadBalancingConfig": [
+				{
+				  "outlier_detection_experimental": {
+					"interval": "0.050s",
+					"baseEjectionTime": "0.100s",
+					"maxEjectionTime": "300s",
+					"maxEjectionPercent": 33,
+					"failurePercentageEjection": {
+						"threshold": 50,
+						"enforcementPercentage": 100,
+						"minimumHosts": 3,
+						"requestVolume": 5
+					},
+					"childPolicy": [{"%s": {}}
+					]
+				  }
+				}
+			  ]
+			}`, leafPolicyName),
 		},
 	}
 	for _, test := range tests {
@@ -273,20 +286,20 @@ func (s) TestNoopConfiguration(t *testing.T) {
 	mr := manual.NewBuilderWithScheme("od-e2e")
 	defer mr.Close()
 
-	noopODServiceConfigJSON := `
-{
-  "loadBalancingConfig": [
-    {
-      "outlier_detection_experimental": {
-        "interval": "0.050s",
-		"baseEjectionTime": "0.100s",
-		"maxEjectionTime": "300s",
-		"maxEjectionPercent": 33,
-        "childPolicy": [{"round_robin": {}}]
-      }
-    }
-  ]
-}`
+	noopODServiceConfigJSON := fmt.Sprintf(`
+	{
+	  "loadBalancingConfig": [
+		{
+		  "outlier_detection_experimental": {
+			"interval": "0.050s",
+			"baseEjectionTime": "0.100s",
+			"maxEjectionTime": "300s",
+			"maxEjectionPercent": 33,
+			"childPolicy": [{"%s": {}}]
+		  }
+		}
+	  ]
+	}`, leafPolicyName)
 	sc := internal.ParseServiceConfig.(func(string) *serviceconfig.ParseResult)(noopODServiceConfigJSON)
 	// The full list of addresses.
 	fullAddresses := []resolver.Address{
@@ -321,26 +334,26 @@ func (s) TestNoopConfiguration(t *testing.T) {
 	// specifies to count RPC's and eject upstreams. Due to the balancer no
 	// longer being a noop, it should eject any unhealthy addresses as specified
 	// by the failure percentage portion of the configuration.
-	countingODServiceConfigJSON := `
-{
-  "loadBalancingConfig": [
-    {
-      "outlier_detection_experimental": {
-        "interval": "0.050s",
-		"baseEjectionTime": "0.100s",
-		"maxEjectionTime": "300s",
-		"maxEjectionPercent": 33,
-		"failurePercentageEjection": {
-			"threshold": 50,
-			"enforcementPercentage": 100,
-			"minimumHosts": 3,
-			"requestVolume": 5
-		},
-        "childPolicy": [{"round_robin": {}}]
-      }
-    }
-  ]
-}`
+	countingODServiceConfigJSON := fmt.Sprintf(`
+	{
+	  "loadBalancingConfig": [
+		{
+		  "outlier_detection_experimental": {
+			"interval": "0.050s",
+			"baseEjectionTime": "0.100s",
+			"maxEjectionTime": "300s",
+			"maxEjectionPercent": 33,
+			"failurePercentageEjection": {
+				"threshold": 50,
+				"enforcementPercentage": 100,
+				"minimumHosts": 3,
+				"requestVolume": 5
+			},
+			"childPolicy": [{"%s": {}}]
+		  }
+		}
+	  ]
+	}`, leafPolicyName)
 	sc = internal.ParseServiceConfig.(func(string) *serviceconfig.ParseResult)(countingODServiceConfigJSON)
 
 	mr.UpdateState(resolver.State{
diff --git a/xds/internal/xdsclient/tests/fallback_test.go b/xds/internal/xdsclient/tests/fallback_test.go
index 18c382db..19f00de4 100644
--- a/xds/internal/xdsclient/tests/fallback_test.go
+++ b/xds/internal/xdsclient/tests/fallback_test.go
@@ -30,7 +30,6 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal"
-	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/stubserver"
 	"google.golang.org/grpc/internal/testutils"
 	"google.golang.org/grpc/internal/testutils/xds/e2e"
@@ -79,11 +78,6 @@ func waitForRPCsToReachBackend(ctx context.Context, client testgrpc.TestServiceC
 // to it. The test also verifies that when all requested resources are cached
 // from the primary, fallback is not triggered when the connection goes down.
 func (s) TestFallback_OnStartup(t *testing.T) {
-	// Enable fallback env var.
-	origFallbackEnv := envconfig.XDSFallbackSupport
-	envconfig.XDSFallbackSupport = true
-	defer func() { envconfig.XDSFallbackSupport = origFallbackEnv }()
-
 	ctx, cancel := context.WithTimeout(context.Background(), defaultFallbackTestTimeout)
 	defer cancel()
 
@@ -248,11 +242,6 @@ func (s) TestFallback_OnStartup(t *testing.T) {
 
 // Tests fallback when the primary management server fails during an update.
 func (s) TestFallback_MidUpdate(t *testing.T) {
-	// Enable fallback env var.
-	origFallbackEnv := envconfig.XDSFallbackSupport
-	envconfig.XDSFallbackSupport = true
-	defer func() { envconfig.XDSFallbackSupport = origFallbackEnv }()
-
 	ctx, cancel := context.WithTimeout(context.Background(), defaultFallbackTestTimeout)
 	defer cancel()
 
@@ -454,11 +443,6 @@ func (s) TestFallback_MidUpdate(t *testing.T) {
 
 // Tests fallback when the primary management server fails during startup.
 func (s) TestFallback_MidStartup(t *testing.T) {
-	// Enable fallback env var.
-	origFallbackEnv := envconfig.XDSFallbackSupport
-	envconfig.XDSFallbackSupport = true
-	defer func() { envconfig.XDSFallbackSupport = origFallbackEnv }()
-
 	ctx, cancel := context.WithTimeout(context.Background(), defaultFallbackTestTimeout)
 	defer cancel()