diff --git a/vendor/google.golang.org/grpc/clientconn.go b/vendor/google.golang.org/grpc/clientconn.go
index 0374920..95a7459 100644
--- a/vendor/google.golang.org/grpc/clientconn.go
+++ b/vendor/google.golang.org/grpc/clientconn.go
@@ -24,7 +24,6 @@
 	"fmt"
 	"math"
 	"net/url"
-	"reflect"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -69,6 +68,9 @@
 	errConnDrain = errors.New("grpc: the connection is drained")
 	// errConnClosing indicates that the connection is closing.
 	errConnClosing = errors.New("grpc: the connection is closing")
+	// errConnIdling indicates the the connection is being closed as the channel
+	// is moving to an idle mode due to inactivity.
+	errConnIdling = errors.New("grpc: the connection is closing due to channel idleness")
 	// invalidDefaultServiceConfigErrPrefix is used to prefix the json parsing error for the default
 	// service config.
 	invalidDefaultServiceConfigErrPrefix = "grpc: the provided default service config is invalid"
@@ -79,7 +81,7 @@
 	// errNoTransportSecurity indicates that there is no transport security
 	// being set for ClientConn. Users should either set one or explicitly
 	// call WithInsecure DialOption to disable security.
-	errNoTransportSecurity = errors.New("grpc: no transport security set (use grpc.WithInsecure() explicitly or set credentials)")
+	errNoTransportSecurity = errors.New("grpc: no transport security set (use grpc.WithTransportCredentials(insecure.NewCredentials()) explicitly or set credentials)")
 	// errTransportCredsAndBundle indicates that creds bundle is used together
 	// with other individual Transport Credentials.
 	errTransportCredsAndBundle = errors.New("grpc: credentials.Bundle may not be used with individual TransportCredentials")
@@ -134,17 +136,43 @@
 // e.g. to use dns resolver, a "dns:///" prefix should be applied to the target.
 func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *ClientConn, err error) {
 	cc := &ClientConn{
-		target:            target,
-		csMgr:             &connectivityStateManager{},
-		conns:             make(map[*addrConn]struct{}),
-		dopts:             defaultDialOptions(),
-		blockingpicker:    newPickerWrapper(),
-		czData:            new(channelzData),
-		firstResolveEvent: grpcsync.NewEvent(),
+		target: target,
+		csMgr:  &connectivityStateManager{},
+		conns:  make(map[*addrConn]struct{}),
+		dopts:  defaultDialOptions(),
+		czData: new(channelzData),
 	}
+
+	// We start the channel off in idle mode, but kick it out of idle at the end
+	// of this method, instead of waiting for the first RPC. Other gRPC
+	// implementations do wait for the first RPC to kick the channel out of
+	// idle. But doing so would be a major behavior change for our users who are
+	// used to seeing the channel active after Dial.
+	//
+	// Taking this approach of kicking it out of idle at the end of this method
+	// allows us to share the code between channel creation and exiting idle
+	// mode. This will also make it easy for us to switch to starting the
+	// channel off in idle, if at all we ever get to do that.
+	cc.idlenessState = ccIdlenessStateIdle
+
 	cc.retryThrottler.Store((*retryThrottler)(nil))
 	cc.safeConfigSelector.UpdateConfigSelector(&defaultConfigSelector{nil})
 	cc.ctx, cc.cancel = context.WithCancel(context.Background())
+	cc.exitIdleCond = sync.NewCond(&cc.mu)
+
+	disableGlobalOpts := false
+	for _, opt := range opts {
+		if _, ok := opt.(*disableGlobalDialOptions); ok {
+			disableGlobalOpts = true
+			break
+		}
+	}
+
+	if !disableGlobalOpts {
+		for _, opt := range globalDialOptions {
+			opt.apply(&cc.dopts)
+		}
+	}
 
 	for _, opt := range opts {
 		opt.apply(&cc.dopts)
@@ -159,43 +187,11 @@
 		}
 	}()
 
-	if channelz.IsOn() {
-		if cc.dopts.channelzParentID != 0 {
-			cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, cc.dopts.channelzParentID, target)
-			channelz.AddTraceEvent(logger, cc.channelzID, 0, &channelz.TraceEventDesc{
-				Desc:     "Channel Created",
-				Severity: channelz.CtInfo,
-				Parent: &channelz.TraceEventDesc{
-					Desc:     fmt.Sprintf("Nested Channel(id:%d) created", cc.channelzID),
-					Severity: channelz.CtInfo,
-				},
-			})
-		} else {
-			cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, 0, target)
-			channelz.Info(logger, cc.channelzID, "Channel Created")
-		}
-		cc.csMgr.channelzID = cc.channelzID
-	}
+	// Register ClientConn with channelz.
+	cc.channelzRegistration(target)
 
-	if cc.dopts.copts.TransportCredentials == nil && cc.dopts.copts.CredsBundle == nil {
-		return nil, errNoTransportSecurity
-	}
-	if cc.dopts.copts.TransportCredentials != nil && cc.dopts.copts.CredsBundle != nil {
-		return nil, errTransportCredsAndBundle
-	}
-	if cc.dopts.copts.CredsBundle != nil && cc.dopts.copts.CredsBundle.TransportCredentials() == nil {
-		return nil, errNoTransportCredsInBundle
-	}
-	transportCreds := cc.dopts.copts.TransportCredentials
-	if transportCreds == nil {
-		transportCreds = cc.dopts.copts.CredsBundle.TransportCredentials()
-	}
-	if transportCreds.Info().SecurityProtocol == "insecure" {
-		for _, cd := range cc.dopts.copts.PerRPCCredentials {
-			if cd.RequireTransportSecurity() {
-				return nil, errTransportCredentialsMissing
-			}
-		}
+	if err := cc.validateTransportCredentials(); err != nil {
+		return nil, err
 	}
 
 	if cc.dopts.defaultServiceConfigRawJSON != nil {
@@ -233,35 +229,19 @@
 		}
 	}()
 
-	scSet := false
-	if cc.dopts.scChan != nil {
-		// Try to get an initial service config.
-		select {
-		case sc, ok := <-cc.dopts.scChan:
-			if ok {
-				cc.sc = &sc
-				cc.safeConfigSelector.UpdateConfigSelector(&defaultConfigSelector{&sc})
-				scSet = true
-			}
-		default:
-		}
-	}
 	if cc.dopts.bs == nil {
 		cc.dopts.bs = backoff.DefaultExponential
 	}
 
 	// Determine the resolver to use.
-	resolverBuilder, err := cc.parseTargetAndFindResolver()
-	if err != nil {
+	if err := cc.parseTargetAndFindResolver(); err != nil {
 		return nil, err
 	}
-	cc.authority, err = determineAuthority(cc.parsedTarget.Endpoint, cc.target, cc.dopts)
-	if err != nil {
+	if err = cc.determineAuthority(); err != nil {
 		return nil, err
 	}
-	channelz.Infof(logger, cc.channelzID, "Channel authority set to %q", cc.authority)
 
-	if cc.dopts.scChan != nil && !scSet {
+	if cc.dopts.scChan != nil {
 		// Blocking wait for the initial service config.
 		select {
 		case sc, ok := <-cc.dopts.scChan:
@@ -277,57 +257,224 @@
 		go cc.scWatcher()
 	}
 
+	// This creates the name resolver, load balancer, blocking picker etc.
+	if err := cc.exitIdleMode(); err != nil {
+		return nil, err
+	}
+
+	// Configure idleness support with configured idle timeout or default idle
+	// timeout duration. Idleness can be explicitly disabled by the user, by
+	// setting the dial option to 0.
+	cc.idlenessMgr = newIdlenessManager(cc, cc.dopts.idleTimeout)
+
+	// Return early for non-blocking dials.
+	if !cc.dopts.block {
+		return cc, nil
+	}
+
+	// A blocking dial blocks until the clientConn is ready.
+	for {
+		s := cc.GetState()
+		if s == connectivity.Idle {
+			cc.Connect()
+		}
+		if s == connectivity.Ready {
+			return cc, nil
+		} else if cc.dopts.copts.FailOnNonTempDialError && s == connectivity.TransientFailure {
+			if err = cc.connectionError(); err != nil {
+				terr, ok := err.(interface {
+					Temporary() bool
+				})
+				if ok && !terr.Temporary() {
+					return nil, err
+				}
+			}
+		}
+		if !cc.WaitForStateChange(ctx, s) {
+			// ctx got timeout or canceled.
+			if err = cc.connectionError(); err != nil && cc.dopts.returnLastError {
+				return nil, err
+			}
+			return nil, ctx.Err()
+		}
+	}
+}
+
+// addTraceEvent is a helper method to add a trace event on the channel. If the
+// channel is a nested one, the same event is also added on the parent channel.
+func (cc *ClientConn) addTraceEvent(msg string) {
+	ted := &channelz.TraceEventDesc{
+		Desc:     fmt.Sprintf("Channel %s", msg),
+		Severity: channelz.CtInfo,
+	}
+	if cc.dopts.channelzParentID != nil {
+		ted.Parent = &channelz.TraceEventDesc{
+			Desc:     fmt.Sprintf("Nested channel(id:%d) %s", cc.channelzID.Int(), msg),
+			Severity: channelz.CtInfo,
+		}
+	}
+	channelz.AddTraceEvent(logger, cc.channelzID, 0, ted)
+}
+
+// exitIdleMode moves the channel out of idle mode by recreating the name
+// resolver and load balancer.
+func (cc *ClientConn) exitIdleMode() error {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return errConnClosing
+	}
+	if cc.idlenessState != ccIdlenessStateIdle {
+		cc.mu.Unlock()
+		logger.Info("ClientConn asked to exit idle mode when not in idle mode")
+		return nil
+	}
+
+	defer func() {
+		// When Close() and exitIdleMode() race against each other, one of the
+		// following two can happen:
+		// - Close() wins the race and runs first. exitIdleMode() runs after, and
+		//   sees that the ClientConn is already closed and hence returns early.
+		// - exitIdleMode() wins the race and runs first and recreates the balancer
+		//   and releases the lock before recreating the resolver. If Close() runs
+		//   in this window, it will wait for exitIdleMode to complete.
+		//
+		// We achieve this synchronization using the below condition variable.
+		cc.mu.Lock()
+		cc.idlenessState = ccIdlenessStateActive
+		cc.exitIdleCond.Signal()
+		cc.mu.Unlock()
+	}()
+
+	cc.idlenessState = ccIdlenessStateExitingIdle
+	exitedIdle := false
+	if cc.blockingpicker == nil {
+		cc.blockingpicker = newPickerWrapper()
+	} else {
+		cc.blockingpicker.exitIdleMode()
+		exitedIdle = true
+	}
+
 	var credsClone credentials.TransportCredentials
 	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
 		credsClone = creds.Clone()
 	}
-	cc.balancerBuildOpts = balancer.BuildOptions{
-		DialCreds:        credsClone,
-		CredsBundle:      cc.dopts.copts.CredsBundle,
-		Dialer:           cc.dopts.copts.Dialer,
-		Authority:        cc.authority,
-		CustomUserAgent:  cc.dopts.copts.UserAgent,
-		ChannelzParentID: cc.channelzID,
-		Target:           cc.parsedTarget,
+	if cc.balancerWrapper == nil {
+		cc.balancerWrapper = newCCBalancerWrapper(cc, balancer.BuildOptions{
+			DialCreds:        credsClone,
+			CredsBundle:      cc.dopts.copts.CredsBundle,
+			Dialer:           cc.dopts.copts.Dialer,
+			Authority:        cc.authority,
+			CustomUserAgent:  cc.dopts.copts.UserAgent,
+			ChannelzParentID: cc.channelzID,
+			Target:           cc.parsedTarget,
+		})
+	} else {
+		cc.balancerWrapper.exitIdleMode()
 	}
-
-	// Build the resolver.
-	rWrapper, err := newCCResolverWrapper(cc, resolverBuilder)
-	if err != nil {
-		return nil, fmt.Errorf("failed to build resolver: %v", err)
-	}
-	cc.mu.Lock()
-	cc.resolverWrapper = rWrapper
+	cc.firstResolveEvent = grpcsync.NewEvent()
 	cc.mu.Unlock()
 
-	// A blocking dial blocks until the clientConn is ready.
-	if cc.dopts.block {
-		for {
-			cc.Connect()
-			s := cc.GetState()
-			if s == connectivity.Ready {
-				break
-			} else if cc.dopts.copts.FailOnNonTempDialError && s == connectivity.TransientFailure {
-				if err = cc.connectionError(); err != nil {
-					terr, ok := err.(interface {
-						Temporary() bool
-					})
-					if ok && !terr.Temporary() {
-						return nil, err
-					}
-				}
-			}
-			if !cc.WaitForStateChange(ctx, s) {
-				// ctx got timeout or canceled.
-				if err = cc.connectionError(); err != nil && cc.dopts.returnLastError {
-					return nil, err
-				}
-				return nil, ctx.Err()
+	// This needs to be called without cc.mu because this builds a new resolver
+	// which might update state or report error inline which needs to be handled
+	// by cc.updateResolverState() which also grabs cc.mu.
+	if err := cc.initResolverWrapper(credsClone); err != nil {
+		return err
+	}
+
+	if exitedIdle {
+		cc.addTraceEvent("exiting idle mode")
+	}
+	return nil
+}
+
+// enterIdleMode puts the channel in idle mode, and as part of it shuts down the
+// name resolver, load balancer and any subchannels.
+func (cc *ClientConn) enterIdleMode() error {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return ErrClientConnClosing
+	}
+	if cc.idlenessState != ccIdlenessStateActive {
+		logger.Error("ClientConn asked to enter idle mode when not active")
+		return nil
+	}
+
+	// cc.conns == nil is a proxy for the ClientConn being closed. So, instead
+	// of setting it to nil here, we recreate the map. This also means that we
+	// don't have to do this when exiting idle mode.
+	conns := cc.conns
+	cc.conns = make(map[*addrConn]struct{})
+
+	// TODO: Currently, we close the resolver wrapper upon entering idle mode
+	// and create a new one upon exiting idle mode. This means that the
+	// `cc.resolverWrapper` field would be overwritten everytime we exit idle
+	// mode. While this means that we need to hold `cc.mu` when accessing
+	// `cc.resolverWrapper`, it makes the code simpler in the wrapper. We should
+	// try to do the same for the balancer and picker wrappers too.
+	cc.resolverWrapper.close()
+	cc.blockingpicker.enterIdleMode()
+	cc.balancerWrapper.enterIdleMode()
+	cc.csMgr.updateState(connectivity.Idle)
+	cc.idlenessState = ccIdlenessStateIdle
+	cc.mu.Unlock()
+
+	go func() {
+		cc.addTraceEvent("entering idle mode")
+		for ac := range conns {
+			ac.tearDown(errConnIdling)
+		}
+	}()
+	return nil
+}
+
+// validateTransportCredentials performs a series of checks on the configured
+// transport credentials. It returns a non-nil error if any of these conditions
+// are met:
+//   - no transport creds and no creds bundle is configured
+//   - both transport creds and creds bundle are configured
+//   - creds bundle is configured, but it lacks a transport credentials
+//   - insecure transport creds configured alongside call creds that require
+//     transport level security
+//
+// If none of the above conditions are met, the configured credentials are
+// deemed valid and a nil error is returned.
+func (cc *ClientConn) validateTransportCredentials() error {
+	if cc.dopts.copts.TransportCredentials == nil && cc.dopts.copts.CredsBundle == nil {
+		return errNoTransportSecurity
+	}
+	if cc.dopts.copts.TransportCredentials != nil && cc.dopts.copts.CredsBundle != nil {
+		return errTransportCredsAndBundle
+	}
+	if cc.dopts.copts.CredsBundle != nil && cc.dopts.copts.CredsBundle.TransportCredentials() == nil {
+		return errNoTransportCredsInBundle
+	}
+	transportCreds := cc.dopts.copts.TransportCredentials
+	if transportCreds == nil {
+		transportCreds = cc.dopts.copts.CredsBundle.TransportCredentials()
+	}
+	if transportCreds.Info().SecurityProtocol == "insecure" {
+		for _, cd := range cc.dopts.copts.PerRPCCredentials {
+			if cd.RequireTransportSecurity() {
+				return errTransportCredentialsMissing
 			}
 		}
 	}
+	return nil
+}
 
-	return cc, nil
+// channelzRegistration registers the newly created ClientConn with channelz and
+// stores the returned identifier in `cc.channelzID` and `cc.csMgr.channelzID`.
+// A channelz trace event is emitted for ClientConn creation. If the newly
+// created ClientConn is a nested one, i.e a valid parent ClientConn ID is
+// specified via a dial option, the trace event is also added to the parent.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) channelzRegistration(target string) {
+	cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, cc.dopts.channelzParentID, target)
+	cc.addTraceEvent("created")
+	cc.csMgr.channelzID = cc.channelzID
 }
 
 // chainUnaryClientInterceptors chains all unary client interceptors into one.
@@ -398,7 +545,7 @@
 	mu         sync.Mutex
 	state      connectivity.State
 	notifyChan chan struct{}
-	channelzID int64
+	channelzID *channelz.Identifier
 }
 
 // updateState updates the connectivity.State of ClientConn.
@@ -464,39 +611,63 @@
 // handshakes. It also handles errors on established connections by
 // re-resolving the name and reconnecting.
 type ClientConn struct {
-	ctx    context.Context
-	cancel context.CancelFunc
+	ctx    context.Context    // Initialized using the background context at dial time.
+	cancel context.CancelFunc // Cancelled on close.
 
-	target       string
-	parsedTarget resolver.Target
-	authority    string
-	dopts        dialOptions
-	csMgr        *connectivityStateManager
+	// The following are initialized at dial time, and are read-only after that.
+	target          string               // User's dial target.
+	parsedTarget    resolver.Target      // See parseTargetAndFindResolver().
+	authority       string               // See determineAuthority().
+	dopts           dialOptions          // Default and user specified dial options.
+	channelzID      *channelz.Identifier // Channelz identifier for the channel.
+	resolverBuilder resolver.Builder     // See parseTargetAndFindResolver().
+	balancerWrapper *ccBalancerWrapper   // Uses gracefulswitch.balancer underneath.
+	idlenessMgr     idlenessManager
 
-	balancerBuildOpts balancer.BuildOptions
-	blockingpicker    *pickerWrapper
-
+	// The following provide their own synchronization, and therefore don't
+	// require cc.mu to be held to access them.
+	csMgr              *connectivityStateManager
+	blockingpicker     *pickerWrapper
 	safeConfigSelector iresolver.SafeConfigSelector
+	czData             *channelzData
+	retryThrottler     atomic.Value // Updated from service config.
 
-	mu              sync.RWMutex
-	resolverWrapper *ccResolverWrapper
-	sc              *ServiceConfig
-	conns           map[*addrConn]struct{}
-	// Keepalive parameter can be updated if a GoAway is received.
-	mkp             keepalive.ClientParameters
-	curBalancerName string
-	balancerWrapper *ccBalancerWrapper
-	retryThrottler  atomic.Value
-
+	// firstResolveEvent is used to track whether the name resolver sent us at
+	// least one update. RPCs block on this event.
 	firstResolveEvent *grpcsync.Event
 
-	channelzID int64 // channelz unique identification number
-	czData     *channelzData
+	// mu protects the following fields.
+	// TODO: split mu so the same mutex isn't used for everything.
+	mu              sync.RWMutex
+	resolverWrapper *ccResolverWrapper         // Initialized in Dial; cleared in Close.
+	sc              *ServiceConfig             // Latest service config received from the resolver.
+	conns           map[*addrConn]struct{}     // Set to nil on close.
+	mkp             keepalive.ClientParameters // May be updated upon receipt of a GoAway.
+	idlenessState   ccIdlenessState            // Tracks idleness state of the channel.
+	exitIdleCond    *sync.Cond                 // Signalled when channel exits idle.
 
 	lceMu               sync.Mutex // protects lastConnectionError
 	lastConnectionError error
 }
 
+// ccIdlenessState tracks the idleness state of the channel.
+//
+// Channels start off in `active` and move to `idle` after a period of
+// inactivity. When moving back to `active` upon an incoming RPC, they
+// transition through `exiting_idle`. This state is useful for synchronization
+// with Close().
+//
+// This state tracking is mostly for self-protection. The idlenessManager is
+// expected to keep track of the state as well, and is expected not to call into
+// the ClientConn unnecessarily.
+type ccIdlenessState int8
+
+const (
+	ccIdlenessStateActive ccIdlenessState = iota
+	ccIdlenessStateIdle
+	ccIdlenessStateExitingIdle
+)
+
 // WaitForStateChange waits until the connectivity.State of ClientConn changes from sourceState or
 // ctx expires. A true value is returned in former case and false in latter.
 //
@@ -536,14 +707,10 @@
 // Notice: This API is EXPERIMENTAL and may be changed or removed in a later
 // release.
 func (cc *ClientConn) Connect() {
-	cc.mu.Lock()
-	defer cc.mu.Unlock()
-	if cc.balancerWrapper != nil && cc.balancerWrapper.exitIdle() {
-		return
-	}
-	for ac := range cc.conns {
-		go ac.connect()
-	}
+	cc.exitIdleMode()
+	// If the ClientConn was not in idle mode, we need to call ExitIdle on the
+	// LB policy so that connections can be created.
+	cc.balancerWrapper.exitIdleMode()
 }
 
 func (cc *ClientConn) scWatcher() {
@@ -623,9 +790,7 @@
 		// with the new addresses.
 		cc.maybeApplyDefaultServiceConfig(nil)
 
-		if cc.balancerWrapper != nil {
-			cc.balancerWrapper.resolverError(err)
-		}
+		cc.balancerWrapper.resolverError(err)
 
 		// No addresses are valid with err set; return early.
 		cc.mu.Unlock()
@@ -653,16 +818,10 @@
 			cc.applyServiceConfigAndBalancer(sc, configSelector, s.Addresses)
 		} else {
 			ret = balancer.ErrBadResolverState
-			if cc.balancerWrapper == nil {
-				var err error
-				if s.ServiceConfig.Err != nil {
-					err = status.Errorf(codes.Unavailable, "error parsing service config: %v", s.ServiceConfig.Err)
-				} else {
-					err = status.Errorf(codes.Unavailable, "illegal service config type: %T", s.ServiceConfig.Config)
-				}
-				cc.safeConfigSelector.UpdateConfigSelector(&defaultConfigSelector{cc.sc})
-				cc.blockingpicker.updatePicker(base.NewErrPicker(err))
-				cc.csMgr.updateState(connectivity.TransientFailure)
+			if cc.sc == nil {
+				// Apply the failing LB only if we haven't received valid service config
+				// from the name resolver in the past.
+				cc.applyFailingLB(s.ServiceConfig)
 				cc.mu.Unlock()
 				return ret
 			}
@@ -670,24 +829,12 @@
 	}
 
 	var balCfg serviceconfig.LoadBalancingConfig
-	if cc.dopts.balancerBuilder == nil && cc.sc != nil && cc.sc.lbConfig != nil {
+	if cc.sc != nil && cc.sc.lbConfig != nil {
 		balCfg = cc.sc.lbConfig.cfg
 	}
-
-	cbn := cc.curBalancerName
 	bw := cc.balancerWrapper
 	cc.mu.Unlock()
-	if cbn != grpclbName {
-		// Filter any grpclb addresses since we don't have the grpclb balancer.
-		for i := 0; i < len(s.Addresses); {
-			if s.Addresses[i].Type == resolver.GRPCLB {
-				copy(s.Addresses[i:], s.Addresses[i+1:])
-				s.Addresses = s.Addresses[:len(s.Addresses)-1]
-				continue
-			}
-			i++
-		}
-	}
+
 	uccsErr := bw.updateClientConnState(&balancer.ClientConnState{ResolverState: s, BalancerConfig: balCfg})
 	if ret == nil {
 		ret = uccsErr // prefer ErrBadResolver state since any other error is
@@ -696,56 +843,28 @@
 	return ret
 }
 
-// switchBalancer starts the switching from current balancer to the balancer
-// with the given name.
-//
-// It will NOT send the current address list to the new balancer. If needed,
-// caller of this function should send address list to the new balancer after
-// this function returns.
+// applyFailingLB is akin to configuring an LB policy on the channel which
+// always fails RPCs. Here, an actual LB policy is not configured, but an always
+// erroring picker is configured, which returns errors with information about
+// what was invalid in the received service config. A config selector with no
+// service config is configured, and the connectivity state of the channel is
+// set to TransientFailure.
 //
 // Caller must hold cc.mu.
-func (cc *ClientConn) switchBalancer(name string) {
-	if strings.EqualFold(cc.curBalancerName, name) {
-		return
-	}
-
-	channelz.Infof(logger, cc.channelzID, "ClientConn switching balancer to %q", name)
-	if cc.dopts.balancerBuilder != nil {
-		channelz.Info(logger, cc.channelzID, "ignoring balancer switching: Balancer DialOption used instead")
-		return
-	}
-	if cc.balancerWrapper != nil {
-		// Don't hold cc.mu while closing the balancers. The balancers may call
-		// methods that require cc.mu (e.g. cc.NewSubConn()). Holding the mutex
-		// would cause a deadlock in that case.
-		cc.mu.Unlock()
-		cc.balancerWrapper.close()
-		cc.mu.Lock()
-	}
-
-	builder := balancer.Get(name)
-	if builder == nil {
-		channelz.Warningf(logger, cc.channelzID, "Channel switches to new LB policy %q due to fallback from invalid balancer name", PickFirstBalancerName)
-		channelz.Infof(logger, cc.channelzID, "failed to get balancer builder for: %v, using pick_first instead", name)
-		builder = newPickfirstBuilder()
+func (cc *ClientConn) applyFailingLB(sc *serviceconfig.ParseResult) {
+	var err error
+	if sc.Err != nil {
+		err = status.Errorf(codes.Unavailable, "error parsing service config: %v", sc.Err)
 	} else {
-		channelz.Infof(logger, cc.channelzID, "Channel switches to new LB policy %q", name)
+		err = status.Errorf(codes.Unavailable, "illegal service config type: %T", sc.Config)
 	}
-
-	cc.curBalancerName = builder.Name()
-	cc.balancerWrapper = newCCBalancerWrapper(cc, builder, cc.balancerBuildOpts)
+	cc.safeConfigSelector.UpdateConfigSelector(&defaultConfigSelector{nil})
+	cc.blockingpicker.updatePicker(base.NewErrPicker(err))
+	cc.csMgr.updateState(connectivity.TransientFailure)
 }
 
 func (cc *ClientConn) handleSubConnStateChange(sc balancer.SubConn, s connectivity.State, err error) {
-	cc.mu.Lock()
-	if cc.conns == nil {
-		cc.mu.Unlock()
-		return
-	}
-	// TODO(bar switching) send updates to all balancer wrappers when balancer
-	// gracefully switching is supported.
-	cc.balancerWrapper.handleSubConnStateChange(sc, s, err)
-	cc.mu.Unlock()
+	cc.balancerWrapper.updateSubConnState(sc, s, err)
 }
 
 // newAddrConn creates an addrConn for addrs and adds it to cc.conns.
@@ -760,27 +879,31 @@
 		dopts:        cc.dopts,
 		czData:       new(channelzData),
 		resetBackoff: make(chan struct{}),
+		stateChan:    make(chan struct{}),
 	}
 	ac.ctx, ac.cancel = context.WithCancel(cc.ctx)
 	// Track ac in cc. This needs to be done before any getTransport(...) is called.
 	cc.mu.Lock()
+	defer cc.mu.Unlock()
 	if cc.conns == nil {
-		cc.mu.Unlock()
 		return nil, ErrClientConnClosing
 	}
-	if channelz.IsOn() {
-		ac.channelzID = channelz.RegisterSubChannel(ac, cc.channelzID, "")
-		channelz.AddTraceEvent(logger, ac.channelzID, 0, &channelz.TraceEventDesc{
-			Desc:     "Subchannel Created",
-			Severity: channelz.CtInfo,
-			Parent: &channelz.TraceEventDesc{
-				Desc:     fmt.Sprintf("Subchannel(id:%d) created", ac.channelzID),
-				Severity: channelz.CtInfo,
-			},
-		})
+
+	var err error
+	ac.channelzID, err = channelz.RegisterSubChannel(ac, cc.channelzID, "")
+	if err != nil {
+		return nil, err
 	}
+	channelz.AddTraceEvent(logger, ac.channelzID, 0, &channelz.TraceEventDesc{
+		Desc:     "Subchannel created",
+		Severity: channelz.CtInfo,
+		Parent: &channelz.TraceEventDesc{
+			Desc:     fmt.Sprintf("Subchannel(id:%d) created", ac.channelzID.Int()),
+			Severity: channelz.CtInfo,
+		},
+	})
+
 	cc.conns[ac] = struct{}{}
-	cc.mu.Unlock()
 	return ac, nil
 }
 
@@ -837,67 +960,93 @@
 func (ac *addrConn) connect() error {
 	ac.mu.Lock()
 	if ac.state == connectivity.Shutdown {
+		if logger.V(2) {
+			logger.Infof("connect called on shutdown addrConn; ignoring.")
+		}
 		ac.mu.Unlock()
 		return errConnClosing
 	}
 	if ac.state != connectivity.Idle {
+		if logger.V(2) {
+			logger.Infof("connect called on addrConn in non-idle state (%v); ignoring.", ac.state)
+		}
 		ac.mu.Unlock()
 		return nil
 	}
-	// Update connectivity state within the lock to prevent subsequent or
-	// concurrent calls from resetting the transport more than once.
-	ac.updateConnectivityState(connectivity.Connecting, nil)
 	ac.mu.Unlock()
 
 	ac.resetTransport()
 	return nil
 }
 
-// tryUpdateAddrs tries to update ac.addrs with the new addresses list.
-//
-// If ac is Connecting, it returns false. The caller should tear down the ac and
-// create a new one. Note that the backoff will be reset when this happens.
-//
-// If ac is TransientFailure, it updates ac.addrs and returns true. The updated
-// addresses will be picked up by retry in the next iteration after backoff.
-//
-// If ac is Shutdown or Idle, it updates ac.addrs and returns true.
-//
-// If ac is Ready, it checks whether current connected address of ac is in the
-// new addrs list.
-//   - If true, it updates ac.addrs and returns true. The ac will keep using
-//     the existing connection.
-//   - If false, it does nothing and returns false.
-func (ac *addrConn) tryUpdateAddrs(addrs []resolver.Address) bool {
+func equalAddresses(a, b []resolver.Address) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, v := range a {
+		if !v.Equal(b[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+// updateAddrs updates ac.addrs with the new addresses list and handles active
+// connections or connection attempts.
+func (ac *addrConn) updateAddrs(addrs []resolver.Address) {
 	ac.mu.Lock()
-	defer ac.mu.Unlock()
-	channelz.Infof(logger, ac.channelzID, "addrConn: tryUpdateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+	channelz.Infof(logger, ac.channelzID, "addrConn: updateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+
+	if equalAddresses(ac.addrs, addrs) {
+		ac.mu.Unlock()
+		return
+	}
+
+	ac.addrs = addrs
+
 	if ac.state == connectivity.Shutdown ||
 		ac.state == connectivity.TransientFailure ||
 		ac.state == connectivity.Idle {
-		ac.addrs = addrs
-		return true
+		// We were not connecting, so do nothing but update the addresses.
+		ac.mu.Unlock()
+		return
 	}
 
-	if ac.state == connectivity.Connecting {
-		return false
-	}
-
-	// ac.state is Ready, try to find the connected address.
-	var curAddrFound bool
-	for _, a := range addrs {
-		a.ServerName = ac.cc.getServerName(a)
-		if reflect.DeepEqual(ac.curAddr, a) {
-			curAddrFound = true
-			break
+	if ac.state == connectivity.Ready {
+		// Try to find the connected address.
+		for _, a := range addrs {
+			a.ServerName = ac.cc.getServerName(a)
+			if a.Equal(ac.curAddr) {
+				// We are connected to a valid address, so do nothing but
+				// update the addresses.
+				ac.mu.Unlock()
+				return
+			}
 		}
 	}
-	channelz.Infof(logger, ac.channelzID, "addrConn: tryUpdateAddrs curAddrFound: %v", curAddrFound)
-	if curAddrFound {
-		ac.addrs = addrs
+
+	// We are either connected to the wrong address or currently connecting.
+	// Stop the current iteration and restart.
+
+	ac.cancel()
+	ac.ctx, ac.cancel = context.WithCancel(ac.cc.ctx)
+
+	// We have to defer here because GracefulClose => Close => onClose, which
+	// requires locking ac.mu.
+	if ac.transport != nil {
+		defer ac.transport.GracefulClose()
+		ac.transport = nil
 	}
 
-	return curAddrFound
+	if len(addrs) == 0 {
+		ac.updateConnectivityState(connectivity.Idle, nil)
+	}
+
+	ac.mu.Unlock()
+
+	// Since we were connecting/connected, we should start a new connection
+	// attempt.
+	go ac.resetTransport()
 }
 
 // getServerName determines the serverName to be used in the connection
@@ -958,15 +1107,11 @@
 	return cc.sc.healthCheckConfig
 }
 
-func (cc *ClientConn) getTransport(ctx context.Context, failfast bool, method string) (transport.ClientTransport, func(balancer.DoneInfo), error) {
-	t, done, err := cc.blockingpicker.pick(ctx, failfast, balancer.PickInfo{
+func (cc *ClientConn) getTransport(ctx context.Context, failfast bool, method string) (transport.ClientTransport, balancer.PickResult, error) {
+	return cc.blockingpicker.pick(ctx, failfast, balancer.PickInfo{
 		Ctx:            ctx,
 		FullMethodName: method,
 	})
-	if err != nil {
-		return nil, nil, toRPCErr(err)
-	}
-	return t, done, nil
 }
 
 func (cc *ClientConn) applyServiceConfigAndBalancer(sc *ServiceConfig, configSelector iresolver.ConfigSelector, addrs []resolver.Address) {
@@ -991,35 +1136,26 @@
 		cc.retryThrottler.Store((*retryThrottler)(nil))
 	}
 
-	if cc.dopts.balancerBuilder == nil {
-		// Only look at balancer types and switch balancer if balancer dial
-		// option is not set.
-		var newBalancerName string
-		if cc.sc != nil && cc.sc.lbConfig != nil {
-			newBalancerName = cc.sc.lbConfig.name
-		} else {
-			var isGRPCLB bool
-			for _, a := range addrs {
-				if a.Type == resolver.GRPCLB {
-					isGRPCLB = true
-					break
-				}
-			}
-			if isGRPCLB {
-				newBalancerName = grpclbName
-			} else if cc.sc != nil && cc.sc.LB != nil {
-				newBalancerName = *cc.sc.LB
-			} else {
-				newBalancerName = PickFirstBalancerName
+	var newBalancerName string
+	if cc.sc != nil && cc.sc.lbConfig != nil {
+		newBalancerName = cc.sc.lbConfig.name
+	} else {
+		var isGRPCLB bool
+		for _, a := range addrs {
+			if a.Type == resolver.GRPCLB {
+				isGRPCLB = true
+				break
 			}
 		}
-		cc.switchBalancer(newBalancerName)
-	} else if cc.balancerWrapper == nil {
-		// Balancer dial option was set, and this is the first time handling
-		// resolved addresses. Build a balancer with dopts.balancerBuilder.
-		cc.curBalancerName = cc.dopts.balancerBuilder.Name()
-		cc.balancerWrapper = newCCBalancerWrapper(cc, cc.dopts.balancerBuilder, cc.balancerBuildOpts)
+		if isGRPCLB {
+			newBalancerName = grpclbName
+		} else if cc.sc != nil && cc.sc.LB != nil {
+			newBalancerName = *cc.sc.LB
+		} else {
+			newBalancerName = PickFirstBalancerName
+		}
 	}
+	cc.balancerWrapper.switchTo(newBalancerName)
 }
 
 func (cc *ClientConn) resolveNow(o resolver.ResolveNowOptions) {
@@ -1063,44 +1199,45 @@
 		cc.mu.Unlock()
 		return ErrClientConnClosing
 	}
+
+	for cc.idlenessState == ccIdlenessStateExitingIdle {
+		cc.exitIdleCond.Wait()
+	}
+
 	conns := cc.conns
 	cc.conns = nil
 	cc.csMgr.updateState(connectivity.Shutdown)
 
+	pWrapper := cc.blockingpicker
 	rWrapper := cc.resolverWrapper
-	cc.resolverWrapper = nil
 	bWrapper := cc.balancerWrapper
-	cc.balancerWrapper = nil
+	idlenessMgr := cc.idlenessMgr
 	cc.mu.Unlock()
 
-	cc.blockingpicker.close()
-
+	// The order of closing matters here since the balancer wrapper assumes the
+	// picker is closed before it is closed.
+	if pWrapper != nil {
+		pWrapper.close()
+	}
 	if bWrapper != nil {
 		bWrapper.close()
 	}
 	if rWrapper != nil {
 		rWrapper.close()
 	}
+	if idlenessMgr != nil {
+		idlenessMgr.close()
+	}
 
 	for ac := range conns {
 		ac.tearDown(ErrClientConnClosing)
 	}
-	if channelz.IsOn() {
-		ted := &channelz.TraceEventDesc{
-			Desc:     "Channel Deleted",
-			Severity: channelz.CtInfo,
-		}
-		if cc.dopts.channelzParentID != 0 {
-			ted.Parent = &channelz.TraceEventDesc{
-				Desc:     fmt.Sprintf("Nested channel(id:%d) deleted", cc.channelzID),
-				Severity: channelz.CtInfo,
-			}
-		}
-		channelz.AddTraceEvent(logger, cc.channelzID, 0, ted)
-		// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add trace reference to
-		// the entity being deleted, and thus prevent it from being deleted right away.
-		channelz.RemoveEntry(cc.channelzID)
-	}
+	cc.addTraceEvent("deleted")
+	// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add
+	// trace reference to the entity being deleted, and thus prevent it from being
+	// deleted right away.
+	channelz.RemoveEntry(cc.channelzID)
+
 	return nil
 }
 
@@ -1125,12 +1262,13 @@
 	addrs   []resolver.Address // All addresses that the resolver resolved to.
 
 	// Use updateConnectivityState for updating addrConn's connectivity state.
-	state connectivity.State
+	state     connectivity.State
+	stateChan chan struct{} // closed and recreated on every state change.
 
 	backoffIdx   int // Needs to be stateful for resetConnectBackoff.
 	resetBackoff chan struct{}
 
-	channelzID int64 // channelz unique identification number.
+	channelzID *channelz.Identifier
 	czData     *channelzData
 }
 
@@ -1139,8 +1277,15 @@
 	if ac.state == s {
 		return
 	}
+	// When changing states, reset the state change channel.
+	close(ac.stateChan)
+	ac.stateChan = make(chan struct{})
 	ac.state = s
-	channelz.Infof(logger, ac.channelzID, "Subchannel Connectivity change to %v", s)
+	if lastErr == nil {
+		channelz.Infof(logger, ac.channelzID, "Subchannel Connectivity change to %v", s)
+	} else {
+		channelz.Infof(logger, ac.channelzID, "Subchannel Connectivity change to %v, last error: %s", s, lastErr)
+	}
 	ac.cc.handleSubConnStateChange(ac.acbw, s, lastErr)
 }
 
@@ -1160,7 +1305,8 @@
 
 func (ac *addrConn) resetTransport() {
 	ac.mu.Lock()
-	if ac.state == connectivity.Shutdown {
+	acCtx := ac.ctx
+	if acCtx.Err() != nil {
 		ac.mu.Unlock()
 		return
 	}
@@ -1188,15 +1334,14 @@
 	ac.updateConnectivityState(connectivity.Connecting, nil)
 	ac.mu.Unlock()
 
-	if err := ac.tryAllAddrs(addrs, connectDeadline); err != nil {
+	if err := ac.tryAllAddrs(acCtx, addrs, connectDeadline); err != nil {
 		ac.cc.resolveNow(resolver.ResolveNowOptions{})
 		// After exhausting all addresses, the addrConn enters
 		// TRANSIENT_FAILURE.
-		ac.mu.Lock()
-		if ac.state == connectivity.Shutdown {
-			ac.mu.Unlock()
+		if acCtx.Err() != nil {
 			return
 		}
+		ac.mu.Lock()
 		ac.updateConnectivityState(connectivity.TransientFailure, err)
 
 		// Backoff.
@@ -1211,13 +1356,13 @@
 			ac.mu.Unlock()
 		case <-b:
 			timer.Stop()
-		case <-ac.ctx.Done():
+		case <-acCtx.Done():
 			timer.Stop()
 			return
 		}
 
 		ac.mu.Lock()
-		if ac.state != connectivity.Shutdown {
+		if acCtx.Err() == nil {
 			ac.updateConnectivityState(connectivity.Idle, err)
 		}
 		ac.mu.Unlock()
@@ -1232,14 +1377,13 @@
 // tryAllAddrs tries to creates a connection to the addresses, and stop when at
 // the first successful one. It returns an error if no address was successfully
 // connected, or updates ac appropriately with the new transport.
-func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.Time) error {
+func (ac *addrConn) tryAllAddrs(ctx context.Context, addrs []resolver.Address, connectDeadline time.Time) error {
 	var firstConnErr error
 	for _, addr := range addrs {
-		ac.mu.Lock()
-		if ac.state == connectivity.Shutdown {
-			ac.mu.Unlock()
+		if ctx.Err() != nil {
 			return errConnClosing
 		}
+		ac.mu.Lock()
 
 		ac.cc.mu.RLock()
 		ac.dopts.copts.KeepaliveParams = ac.cc.mkp
@@ -1253,7 +1397,7 @@
 
 		channelz.Infof(logger, ac.channelzID, "Subchannel picks a new address %q to connect", addr.Addr)
 
-		err := ac.createTransport(addr, copts, connectDeadline)
+		err := ac.createTransport(ctx, addr, copts, connectDeadline)
 		if err == nil {
 			return nil
 		}
@@ -1270,113 +1414,84 @@
 // createTransport creates a connection to addr. It returns an error if the
 // address was not successfully connected, or updates ac appropriately with the
 // new transport.
-func (ac *addrConn) createTransport(addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) error {
-	// TODO: Delete prefaceReceived and move the logic to wait for it into the
-	// transport.
-	prefaceReceived := grpcsync.NewEvent()
-	connClosed := grpcsync.NewEvent()
-
+func (ac *addrConn) createTransport(ctx context.Context, addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) error {
 	addr.ServerName = ac.cc.getServerName(addr)
-	hctx, hcancel := context.WithCancel(ac.ctx)
-	hcStarted := false // protected by ac.mu
+	hctx, hcancel := context.WithCancel(ctx)
 
-	onClose := func() {
+	onClose := func(r transport.GoAwayReason) {
 		ac.mu.Lock()
 		defer ac.mu.Unlock()
-		defer connClosed.Fire()
-		if !hcStarted || hctx.Err() != nil {
-			// We didn't start the health check or set the state to READY, so
-			// no need to do anything else here.
-			//
-			// OR, we have already cancelled the health check context, meaning
-			// we have already called onClose once for this transport.  In this
-			// case it would be dangerous to clear the transport and update the
-			// state, since there may be a new transport in this addrConn.
+		// adjust params based on GoAwayReason
+		ac.adjustParams(r)
+		if ctx.Err() != nil {
+			// Already shut down or connection attempt canceled.  tearDown() or
+			// updateAddrs() already cleared the transport and canceled hctx
+			// via ac.ctx, and we expected this connection to be closed, so do
+			// nothing here.
 			return
 		}
 		hcancel()
-		ac.transport = nil
-		// Refresh the name resolver
-		ac.cc.resolveNow(resolver.ResolveNowOptions{})
-		if ac.state != connectivity.Shutdown {
-			ac.updateConnectivityState(connectivity.Idle, nil)
+		if ac.transport == nil {
+			// We're still connecting to this address, which could error.  Do
+			// not update the connectivity state or resolve; these will happen
+			// at the end of the tryAllAddrs connection loop in the event of an
+			// error.
+			return
 		}
+		ac.transport = nil
+		// Refresh the name resolver on any connection loss.
+		ac.cc.resolveNow(resolver.ResolveNowOptions{})
+		// Always go idle and wait for the LB policy to initiate a new
+		// connection attempt.
+		ac.updateConnectivityState(connectivity.Idle, nil)
 	}
 
-	onGoAway := func(r transport.GoAwayReason) {
-		ac.mu.Lock()
-		ac.adjustParams(r)
-		ac.mu.Unlock()
-		onClose()
-	}
-
-	connectCtx, cancel := context.WithDeadline(ac.ctx, connectDeadline)
+	connectCtx, cancel := context.WithDeadline(ctx, connectDeadline)
 	defer cancel()
-	if channelz.IsOn() {
-		copts.ChannelzParentID = ac.channelzID
-	}
+	copts.ChannelzParentID = ac.channelzID
 
-	newTr, err := transport.NewClientTransport(connectCtx, ac.cc.ctx, addr, copts, func() { prefaceReceived.Fire() }, onGoAway, onClose)
+	newTr, err := transport.NewClientTransport(connectCtx, ac.cc.ctx, addr, copts, onClose)
 	if err != nil {
+		if logger.V(2) {
+			logger.Infof("Creating new client transport to %q: %v", addr, err)
+		}
 		// newTr is either nil, or closed.
-		channelz.Warningf(logger, ac.channelzID, "grpc: addrConn.createTransport failed to connect to %v. Err: %v", addr, err)
+		hcancel()
+		channelz.Warningf(logger, ac.channelzID, "grpc: addrConn.createTransport failed to connect to %s. Err: %v", addr, err)
 		return err
 	}
 
-	select {
-	case <-connectCtx.Done():
-		// We didn't get the preface in time.
+	ac.mu.Lock()
+	defer ac.mu.Unlock()
+	if ctx.Err() != nil {
+		// This can happen if the subConn was removed while in `Connecting`
+		// state. tearDown() would have set the state to `Shutdown`, but
+		// would not have closed the transport since ac.transport would not
+		// have been set at that point.
+		//
+		// We run this in a goroutine because newTr.Close() calls onClose()
+		// inline, which requires locking ac.mu.
+		//
 		// The error we pass to Close() is immaterial since there are no open
 		// streams at this point, so no trailers with error details will be sent
 		// out. We just need to pass a non-nil error.
-		newTr.Close(transport.ErrConnClosing)
-		if connectCtx.Err() == context.DeadlineExceeded {
-			err := errors.New("failed to receive server preface within timeout")
-			channelz.Warningf(logger, ac.channelzID, "grpc: addrConn.createTransport failed to connect to %v: %v", addr, err)
-			return err
-		}
+		//
+		// This can also happen when updateAddrs is called during a connection
+		// attempt.
+		go newTr.Close(transport.ErrConnClosing)
 		return nil
-	case <-prefaceReceived.Done():
-		// We got the preface - huzzah! things are good.
-		ac.mu.Lock()
-		defer ac.mu.Unlock()
-		if connClosed.HasFired() {
-			// onClose called first; go idle but do nothing else.
-			if ac.state != connectivity.Shutdown {
-				ac.updateConnectivityState(connectivity.Idle, nil)
-			}
-			return nil
-		}
-		if ac.state == connectivity.Shutdown {
-			// This can happen if the subConn was removed while in `Connecting`
-			// state. tearDown() would have set the state to `Shutdown`, but
-			// would not have closed the transport since ac.transport would not
-			// been set at that point.
-			//
-			// We run this in a goroutine because newTr.Close() calls onClose()
-			// inline, which requires locking ac.mu.
-			//
-			// The error we pass to Close() is immaterial since there are no open
-			// streams at this point, so no trailers with error details will be sent
-			// out. We just need to pass a non-nil error.
-			go newTr.Close(transport.ErrConnClosing)
-			return nil
-		}
-		ac.curAddr = addr
-		ac.transport = newTr
-		hcStarted = true
-		ac.startHealthCheck(hctx) // Will set state to READY if appropriate.
-		return nil
-	case <-connClosed.Done():
-		// The transport has already closed.  If we received the preface, too,
-		// this is not an error.
-		select {
-		case <-prefaceReceived.Done():
-			return nil
-		default:
-			return errors.New("connection closed before server preface received")
-		}
 	}
+	if hctx.Err() != nil {
+		// onClose was already called for this connection, but the connection
+		// was successfully established first.  Consider it a success and set
+		// the new state to Idle.
+		ac.updateConnectivityState(connectivity.Idle, nil)
+		return nil
+	}
+	ac.curAddr = addr
+	ac.transport = newTr
+	ac.startHealthCheck(hctx) // Will set state to READY if appropriate.
+	return nil
 }
 
 // startHealthCheck starts the health checking stream (RPC) to watch the health
@@ -1446,7 +1561,7 @@
 			if status.Code(err) == codes.Unimplemented {
 				channelz.Error(logger, ac.channelzID, "Subchannel health check is unimplemented at server side, thus health check is disabled")
 			} else {
-				channelz.Errorf(logger, ac.channelzID, "HealthCheckFunc exits with unexpected error %v", err)
+				channelz.Errorf(logger, ac.channelzID, "Health checking failed: %v", err)
 			}
 		}
 	}()
@@ -1470,6 +1585,29 @@
 	return nil
 }
 
+// getTransport waits until the addrconn is ready and returns the transport.
+// If the context expires first, returns an appropriate status.  If the
+// addrConn is stopped first, returns an Unavailable status error.
+func (ac *addrConn) getTransport(ctx context.Context) (transport.ClientTransport, error) {
+	for ctx.Err() == nil {
+		ac.mu.Lock()
+		t, state, sc := ac.transport, ac.state, ac.stateChan
+		ac.mu.Unlock()
+		if state == connectivity.Ready {
+			return t, nil
+		}
+		if state == connectivity.Shutdown {
+			return nil, status.Errorf(codes.Unavailable, "SubConn shutting down")
+		}
+
+		select {
+		case <-ctx.Done():
+		case <-sc:
+		}
+	}
+	return nil, status.FromContextError(ctx.Err()).Err()
+}
+
 // tearDown starts to tear down the addrConn.
 //
 // Note that tearDown doesn't remove ac from ac.cc.conns, so the addrConn struct
@@ -1497,19 +1635,18 @@
 		curTr.GracefulClose()
 		ac.mu.Lock()
 	}
-	if channelz.IsOn() {
-		channelz.AddTraceEvent(logger, ac.channelzID, 0, &channelz.TraceEventDesc{
-			Desc:     "Subchannel Deleted",
+	channelz.AddTraceEvent(logger, ac.channelzID, 0, &channelz.TraceEventDesc{
+		Desc:     "Subchannel deleted",
+		Severity: channelz.CtInfo,
+		Parent: &channelz.TraceEventDesc{
+			Desc:     fmt.Sprintf("Subchannel(id:%d) deleted", ac.channelzID.Int()),
 			Severity: channelz.CtInfo,
-			Parent: &channelz.TraceEventDesc{
-				Desc:     fmt.Sprintf("Subchanel(id:%d) deleted", ac.channelzID),
-				Severity: channelz.CtInfo,
-			},
-		})
-		// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add trace reference to
-		// the entity being deleted, and thus prevent it from being deleted right away.
-		channelz.RemoveEntry(ac.channelzID)
-	}
+		},
+	})
+	// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add
+	// trace reference to the entity being deleted, and thus prevent it from
+	// being deleted right away.
+	channelz.RemoveEntry(ac.channelzID)
 	ac.mu.Unlock()
 }
 
@@ -1598,6 +1735,9 @@
 // referenced by users.
 var ErrClientConnTimeout = errors.New("grpc: timed out when dialing")
 
+// getResolver finds the scheme in the cc's resolvers or the global registry.
+// scheme should always be lowercase (typically by virtue of url.Parse()
+// performing proper RFC3986 behavior).
 func (cc *ClientConn) getResolver(scheme string) resolver.Builder {
 	for _, rb := range cc.dopts.resolvers {
 		if scheme == rb.Scheme() {
@@ -1619,7 +1759,14 @@
 	return cc.lastConnectionError
 }
 
-func (cc *ClientConn) parseTargetAndFindResolver() (resolver.Builder, error) {
+// parseTargetAndFindResolver parses the user's dial target and stores the
+// parsed target in `cc.parsedTarget`.
+//
+// The resolver to use is determined based on the scheme in the parsed target
+// and the same is stored in `cc.resolverBuilder`.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) parseTargetAndFindResolver() error {
 	channelz.Infof(logger, cc.channelzID, "original dial target is: %q", cc.target)
 
 	var rb resolver.Builder
@@ -1628,10 +1775,11 @@
 		channelz.Infof(logger, cc.channelzID, "dial target %q parse failed: %v", cc.target, err)
 	} else {
 		channelz.Infof(logger, cc.channelzID, "parsed dial target is: %+v", parsedTarget)
-		rb = cc.getResolver(parsedTarget.Scheme)
+		rb = cc.getResolver(parsedTarget.URL.Scheme)
 		if rb != nil {
 			cc.parsedTarget = parsedTarget
-			return rb, nil
+			cc.resolverBuilder = rb
+			return nil
 		}
 	}
 
@@ -1646,42 +1794,30 @@
 	parsedTarget, err = parseTarget(canonicalTarget)
 	if err != nil {
 		channelz.Infof(logger, cc.channelzID, "dial target %q parse failed: %v", canonicalTarget, err)
-		return nil, err
+		return err
 	}
 	channelz.Infof(logger, cc.channelzID, "parsed dial target is: %+v", parsedTarget)
-	rb = cc.getResolver(parsedTarget.Scheme)
+	rb = cc.getResolver(parsedTarget.URL.Scheme)
 	if rb == nil {
-		return nil, fmt.Errorf("could not get resolver for default scheme: %q", parsedTarget.Scheme)
+		return fmt.Errorf("could not get resolver for default scheme: %q", parsedTarget.URL.Scheme)
 	}
 	cc.parsedTarget = parsedTarget
-	return rb, nil
+	cc.resolverBuilder = rb
+	return nil
 }
 
 // parseTarget uses RFC 3986 semantics to parse the given target into a
-// resolver.Target struct containing scheme, authority and endpoint. Query
+// resolver.Target struct containing scheme, authority and url. Query
 // params are stripped from the endpoint.
 func parseTarget(target string) (resolver.Target, error) {
 	u, err := url.Parse(target)
 	if err != nil {
 		return resolver.Target{}, err
 	}
-	// For targets of the form "[scheme]://[authority]/endpoint, the endpoint
-	// value returned from url.Parse() contains a leading "/". Although this is
-	// in accordance with RFC 3986, we do not want to break existing resolver
-	// implementations which expect the endpoint without the leading "/". So, we
-	// end up stripping the leading "/" here. But this will result in an
-	// incorrect parsing for something like "unix:///path/to/socket". Since we
-	// own the "unix" resolver, we can workaround in the unix resolver by using
-	// the `URL` field instead of the `Endpoint` field.
-	endpoint := u.Path
-	if endpoint == "" {
-		endpoint = u.Opaque
-	}
-	endpoint = strings.TrimPrefix(endpoint, "/")
+
 	return resolver.Target{
 		Scheme:    u.Scheme,
 		Authority: u.Host,
-		Endpoint:  endpoint,
 		URL:       *u,
 	}, nil
 }
@@ -1690,7 +1826,15 @@
 // - user specified authority override using `WithAuthority` dial option
 // - creds' notion of server name for the authentication handshake
 // - endpoint from dial target of the form "scheme://[authority]/endpoint"
-func determineAuthority(endpoint, target string, dopts dialOptions) (string, error) {
+//
+// Stores the determined authority in `cc.authority`.
+//
+// Returns a non-nil error if the authority returned by the transport
+// credentials do not match the authority configured through the dial option.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) determineAuthority() error {
+	dopts := cc.dopts
 	// Historically, we had two options for users to specify the serverName or
 	// authority for a channel. One was through the transport credentials
 	// (either in its constructor, or through the OverrideServerName() method).
@@ -1707,25 +1851,58 @@
 	}
 	authorityFromDialOption := dopts.authority
 	if (authorityFromCreds != "" && authorityFromDialOption != "") && authorityFromCreds != authorityFromDialOption {
-		return "", fmt.Errorf("ClientConn's authority from transport creds %q and dial option %q don't match", authorityFromCreds, authorityFromDialOption)
+		return fmt.Errorf("ClientConn's authority from transport creds %q and dial option %q don't match", authorityFromCreds, authorityFromDialOption)
 	}
 
+	endpoint := cc.parsedTarget.Endpoint()
+	target := cc.target
 	switch {
 	case authorityFromDialOption != "":
-		return authorityFromDialOption, nil
+		cc.authority = authorityFromDialOption
 	case authorityFromCreds != "":
-		return authorityFromCreds, nil
+		cc.authority = authorityFromCreds
 	case strings.HasPrefix(target, "unix:") || strings.HasPrefix(target, "unix-abstract:"):
 		// TODO: remove when the unix resolver implements optional interface to
 		// return channel authority.
-		return "localhost", nil
+		cc.authority = "localhost"
 	case strings.HasPrefix(endpoint, ":"):
-		return "localhost" + endpoint, nil
+		cc.authority = "localhost" + endpoint
 	default:
 		// TODO: Define an optional interface on the resolver builder to return
 		// the channel authority given the user's dial target. For resolvers
 		// which don't implement this interface, we will use the endpoint from
 		// "scheme://authority/endpoint" as the default authority.
-		return endpoint, nil
+		cc.authority = endpoint
 	}
+	channelz.Infof(logger, cc.channelzID, "Channel authority set to %q", cc.authority)
+	return nil
+}
+
+// initResolverWrapper creates a ccResolverWrapper, which builds the name
+// resolver. This method grabs the lock to assign the newly built resolver
+// wrapper to the cc.resolverWrapper field.
+func (cc *ClientConn) initResolverWrapper(creds credentials.TransportCredentials) error {
+	rw, err := newCCResolverWrapper(cc, ccResolverWrapperOpts{
+		target:  cc.parsedTarget,
+		builder: cc.resolverBuilder,
+		bOpts: resolver.BuildOptions{
+			DisableServiceConfig: cc.dopts.disableServiceConfig,
+			DialCreds:            creds,
+			CredsBundle:          cc.dopts.copts.CredsBundle,
+			Dialer:               cc.dopts.copts.Dialer,
+		},
+		channelzID: cc.channelzID,
+	})
+	if err != nil {
+		return fmt.Errorf("failed to build resolver: %v", err)
+	}
+	// Resolver implementations may report state update or error inline when
+	// built (or right after), and this is handled in cc.updateResolverState.
+	// Also, an error from the resolver might lead to a re-resolution request
+	// from the balancer, which is handled in resolveNow() where
+	// `cc.resolverWrapper` is accessed. Hence, we need to hold the lock here.
+	cc.mu.Lock()
+	cc.resolverWrapper = rw
+	cc.mu.Unlock()
+	return nil
 }