func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	if initFakeZK != nil {
		initFakeZK()
	}
	ts := topo.GetServer()
	defer topo.CloseServers()

	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*connTimeoutTotal, *healthCheckRetryDelay, *healthCheckTimeout, "" /* statsSuffix */)

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	vtg := vtgate.Init(context.Background(), healthCheck, ts, resilientSrvTopoServer, *cell, *retryDelay, *retryCount, *connTimeoutTotal, *connTimeoutPerConn, *connLife, tabletTypes, *maxInFlight, *testGateway)

	servenv.OnRun(func() {
		addStatusParts(vtg)
	})
	servenv.RunDefault()
}

// startHealthWatchers launches the topology watchers and health checking to monitor
// all tablets on the shard. Function should be called before the start of the schema
// swap process.
func (shardSwap *shardSchemaSwap) startHealthWatchers() error {
	shardSwap.tabletHealthCheck = discovery.NewHealthCheck(
		*vtctl.HealthCheckTopologyRefresh, *vtctl.HealthcheckRetryDelay, *vtctl.HealthCheckTimeout)
	shardSwap.tabletHealthCheck.SetListener(shardSwap, true /* sendDownEvents */)

	topoServer := shardSwap.parent.topoServer
	cellList, err := topoServer.GetKnownCells(shardSwap.parent.ctx)
	if err != nil {
		return err
	}
	for _, cell := range cellList {
		watcher := discovery.NewShardReplicationWatcher(
			topoServer,
			shardSwap.tabletHealthCheck,
			cell,
			shardSwap.parent.keyspace,
			shardSwap.shardName,
			*vtctl.HealthCheckTimeout,
			discovery.DefaultTopoReadConcurrency)
		shardSwap.tabletWatchers = append(shardSwap.tabletWatchers, watcher)
	}
	for _, watcher := range shardSwap.tabletWatchers {
		if err := watcher.WaitForInitialTopology(); err != nil {
			return err
		}
	}
	shardSwap.tabletHealthCheck.WaitForInitialStatsUpdates()
	return nil
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	ts := topo.GetServer()
	defer topo.CloseServers()

	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*healthCheckConnTimeout, *healthCheckRetryDelay, *healthCheckTimeout)
	healthCheck.RegisterStats()

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	l2vtg := l2vtgate.Init(healthCheck, ts, resilientSrvTopoServer, *cell, *retryCount, tabletTypes)

	servenv.OnRun(func() {
		addStatusParts(l2vtg)
	})
	servenv.RunDefault()
}

func newRealtimeStats(ts topo.Server) (*realtimeStats, error) {
	hc := discovery.NewHealthCheck(*vtctl.HealthCheckTimeout, *vtctl.HealthcheckRetryDelay, *vtctl.HealthCheckTimeout)
	tabletStatsCache := &tabletStatsCache{
		statuses: make(map[string]map[string]*discovery.TabletStats),
	}
	hc.SetListener(tabletStatsCache)
	r := &realtimeStats{
		healthCheck: hc,
		tabletStats: tabletStatsCache,
	}

	// Get the list of all tablets from all cells and monitor the topology for added or removed tablets with a CellTabletsWatcher.
	cells, err := ts.GetKnownCells(context.Background())
	if err != nil {
		return r, fmt.Errorf("error when getting cells: %v", err)
	}
	var watchers []*discovery.TopologyWatcher
	for _, cell := range cells {
		watcher := discovery.NewCellTabletsWatcher(ts, hc, cell, *vtctl.HealthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
		watchers = append(watchers, watcher)
	}
	r.cellWatchers = watchers

	return r, nil
}

// FindHealthyRdonlyEndPoint returns a random healthy endpoint.
// Since we don't want to use them all, we require at least
// minHealthyEndPoints servers to be healthy.
// May block up to -wait_for_healthy_rdonly_endpoints_timeout.
func FindHealthyRdonlyEndPoint(ctx context.Context, wr *wrangler.Wrangler, cell, keyspace, shard string) (*topodatapb.TabletAlias, error) {
	busywaitCtx, busywaitCancel := context.WithTimeout(ctx, *WaitForHealthyEndPointsTimeout)
	defer busywaitCancel()

	// create a discovery healthcheck, wait for it to have one rdonly
	// endpoints at this point
	healthCheck := discovery.NewHealthCheck(*remoteActionsTimeout, *healthcheckRetryDelay, *healthCheckTimeout, "" /* statsSuffix */)
	watcher := discovery.NewShardReplicationWatcher(wr.TopoServer(), healthCheck, cell, keyspace, shard, *healthCheckTopologyRefresh, 5 /*topoReadConcurrency*/)
	defer watcher.Stop()
	defer healthCheck.Close()
	if err := discovery.WaitForEndPoints(ctx, healthCheck, cell, keyspace, shard, []topodatapb.TabletType{topodatapb.TabletType_RDONLY}); err != nil {
		return nil, fmt.Errorf("error waiting for rdonly endpoints for (%v,%v/%v): %v", cell, keyspace, shard, err)
	}

	var healthyEndpoints []*topodatapb.EndPoint
	for {
		select {
		case <-busywaitCtx.Done():
			return nil, fmt.Errorf("Not enough endpoints to choose from in (%v,%v/%v), have %v healthy ones, need at least %v Context Error: %v", cell, keyspace, shard, len(healthyEndpoints), *minHealthyEndPoints, busywaitCtx.Err())
		default:
		}

		addrs := healthCheck.GetEndPointStatsFromTarget(keyspace, shard, topodatapb.TabletType_RDONLY)
		healthyEndpoints = make([]*topodatapb.EndPoint, 0, len(addrs))
		for _, addr := range addrs {
			// Note we do not check the 'Serving' flag here.
			// This is mainly to avoid the case where we run a
			// Diff between a source and destination, and the source
			// is not serving (disabled by TabletControl).
			// When we switch the tablet to 'worker', it will
			// go back to serving state.
			if addr.Stats == nil || addr.Stats.HealthError != "" || addr.Stats.SecondsBehindMaster > 30 {
				continue
			}
			healthyEndpoints = append(healthyEndpoints, addr.EndPoint)
		}

		if len(healthyEndpoints) >= *minHealthyEndPoints {
			break
		}

		deadlineForLog, _ := busywaitCtx.Deadline()
		wr.Logger().Infof("Waiting for enough endpoints to become available. available: %v required: %v Waiting up to %.1f more seconds.", len(healthyEndpoints), *minHealthyEndPoints, deadlineForLog.Sub(time.Now()).Seconds())
		// Block for 1 second because 2 seconds is the -health_check_interval flag value in integration tests.
		timer := time.NewTimer(1 * time.Second)
		select {
		case <-busywaitCtx.Done():
			timer.Stop()
		case <-timer.C:
		}
	}

	// random server in the list is what we want
	index := rand.Intn(len(healthyEndpoints))
	return &topodatapb.TabletAlias{
		Cell: cell,
		Uid:  healthyEndpoints[index].Uid,
	}, nil
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	if initFakeZK != nil {
		initFakeZK()
	}
	ts := topo.GetServer()
	defer topo.CloseServers()

	var schema *planbuilder.Schema
	if *schemaFile != "" {
		var err error
		if schema, err = planbuilder.LoadFile(*schemaFile); err != nil {
			log.Error(err)
			exit.Return(1)
		}
		log.Infof("v3 is enabled: loaded schema from file: %v", *schemaFile)
	} else {
		ctx := context.Background()
		schemaJSON, err := ts.GetVSchema(ctx)
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		schema, err = planbuilder.NewSchema([]byte(schemaJSON))
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		log.Infof("v3 is enabled: loaded schema from topo")
	}

startServer:
	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*connTimeoutTotal, *healthCheckRetryDelay, *healthCheckTimeout, "" /* statsSuffix */)

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	vtg := vtgate.Init(healthCheck, ts, resilientSrvTopoServer, schema, *cell, *retryDelay, *retryCount, *connTimeoutTotal, *connTimeoutPerConn, *connLife, tabletTypes, *maxInFlight, *testGateway)

	servenv.OnRun(func() {
		addStatusParts(vtg)
	})
	servenv.RunDefault()
}

func main() {
	defer exit.Recover()

	// flag parsing
	flags := dbconfigs.AppConfig | dbconfigs.DbaConfig |
		dbconfigs.FilteredConfig | dbconfigs.ReplConfig
	dbconfigs.RegisterFlags(flags)
	mysqlctl.RegisterFlags()
	flag.Parse()
	if len(flag.Args()) > 0 {
		flag.Usage()
		log.Errorf("vtcombo doesn't take any positional arguments")
		exit.Return(1)
	}

	// register topo server
	topo.RegisterServer("fakezk", zktopo.NewServer(fakezk.NewConn()))
	ts := topo.GetServerByName("fakezk")

	servenv.Init()

	// database configs
	mycnf, err := mysqlctl.NewMycnfFromFlags(0)
	if err != nil {
		log.Errorf("mycnf read failed: %v", err)
		exit.Return(1)
	}
	dbcfgs, err := dbconfigs.Init(mycnf.SocketFile, flags)
	if err != nil {
		log.Warning(err)
	}
	mysqld := mysqlctl.NewMysqld("Dba", "App", mycnf, &dbcfgs.Dba, &dbcfgs.App.ConnParams, &dbcfgs.Repl)

	// tablets configuration and init
	binlog.RegisterUpdateStreamService(mycnf)
	initTabletMap(ts, *topology, mysqld, dbcfgs, mycnf)

	// vtgate configuration and init
	resilientSrvTopoServer := vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")
	healthCheck := discovery.NewHealthCheck(30*time.Second /*connTimeoutTotal*/, 1*time.Millisecond /*retryDelay*/)
	vtgate.Init(healthCheck, ts, resilientSrvTopoServer, nil /*schema*/, cell, 1*time.Millisecond /*retryDelay*/, 2 /*retryCount*/, 30*time.Second /*connTimeoutTotal*/, 10*time.Second /*connTimeoutPerConn*/, 365*24*time.Hour /*connLife*/, 0 /*maxInFlight*/, "" /*testGateway*/)

	servenv.OnTerm(func() {
		// FIXME(alainjobart) stop vtgate, all tablets
		//		qsc.DisallowQueries()
		//		agent.Stop()
	})
	servenv.OnClose(func() {
		// We will still use the topo server during lameduck period
		// to update our state, so closing it in OnClose()
		topo.CloseServers()
	})
	servenv.RunDefault()
}

// TestGRPCDiscovery tests the discovery gateway with a gRPC
// connection from the gateway to the fake tablet.
func TestGRPCDiscovery(t *testing.T) {
	flag.Set("tablet_protocol", "grpc")
	flag.Set("gateway_implementation", "discoverygateway")

	// Fake services for the tablet, topo server.
	service, ts, cell := CreateFakeServers(t)

	// Tablet: listen on a random port.
	listener, err := net.Listen("tcp", ":0")
	if err != nil {
		t.Fatalf("Cannot listen: %v", err)
	}
	host := listener.Addr().(*net.TCPAddr).IP.String()
	port := listener.Addr().(*net.TCPAddr).Port
	defer listener.Close()

	// Tablet: create a gRPC server and listen on the port.
	server := grpc.NewServer()
	grpcqueryservice.Register(server, service)
	go server.Serve(listener)
	defer server.Stop()

	// VTGate: create the discovery healthcheck, and the gateway.
	// Wait for the right tablets to be present.
	hc := discovery.NewHealthCheck(30*time.Second, 10*time.Second, 2*time.Minute)
	dg := gateway.GetCreator()(hc, ts, ts, cell, 2)
	hc.AddTablet(&topodatapb.Tablet{
		Alias: &topodatapb.TabletAlias{
			Cell: cell,
			Uid:  43,
		},
		Keyspace: tabletconntest.TestTarget.Keyspace,
		Shard:    tabletconntest.TestTarget.Shard,
		Type:     tabletconntest.TestTarget.TabletType,
		Hostname: host,
		PortMap: map[string]int32{
			"grpc": int32(port),
		},
	}, "test_tablet")
	err = gateway.WaitForTablets(dg, []topodatapb.TabletType{tabletconntest.TestTarget.TabletType})
	if err != nil {
		t.Fatalf("WaitForTablets failed: %v", err)
	}
	defer dg.Close(context.Background())

	// run the test suite.
	TestSuite(t, "discovery-grpc", dg, service)

	// run it again with vtgate combining Begin and Execute
	flag.Set("tablet_grpc_combine_begin_execute", "true")
	TestSuite(t, "discovery-grpc-combo", dg, service)
}

// init phase:
// - read the destination keyspace, make sure it has 'servedFrom' values
func (scw *SplitCloneWorker) init(ctx context.Context) error {
	scw.setState(WorkerStateInit)

	// read the keyspace and validate it
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	var err error
	scw.destinationKeyspaceInfo, err = scw.wr.TopoServer().GetKeyspace(shortCtx, scw.destinationKeyspace)
	cancel()
	if err != nil {
		return fmt.Errorf("cannot read (destination) keyspace %v: %v", scw.destinationKeyspace, err)
	}

	// Set source and destination shard infos.
	switch scw.cloneType {
	case horizontalResharding:
		if err := scw.initShardsForHorizontalResharding(ctx); err != nil {
			return err
		}
	case verticalSplit:
		if err := scw.initShardsForVerticalSplit(ctx); err != nil {
			return err
		}
	}

	if err := scw.sanityCheckShardInfos(); err != nil {
		return err
	}

	if scw.cloneType == horizontalResharding {
		if err := scw.loadVSchema(ctx); err != nil {
			return err
		}
	}

	// Initialize healthcheck and add destination shards to it.
	scw.healthCheck = discovery.NewHealthCheck(*remoteActionsTimeout, *healthcheckRetryDelay, *healthCheckTimeout)
	scw.tsc = discovery.NewTabletStatsCacheDoNotSetListener(scw.cell)
	// We set sendDownEvents=true because it's required by TabletStatsCache.
	scw.healthCheck.SetListener(scw, true /* sendDownEvents */)

	// Start watchers to get tablets added automatically to healthCheck.
	allShards := append(scw.sourceShards, scw.destinationShards...)
	for _, si := range allShards {
		watcher := discovery.NewShardReplicationWatcher(scw.wr.TopoServer(), scw.healthCheck,
			scw.cell, si.Keyspace(), si.ShardName(),
			*healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
		scw.shardWatchers = append(scw.shardWatchers, watcher)
	}

	return nil
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	if initFakeZK != nil {
		initFakeZK()
	}
	ts := topo.GetServer()
	defer topo.CloseServers()

	var schema *planbuilder.Schema
	if *schemaFile != "" {
		var err error
		if schema, err = planbuilder.LoadFile(*schemaFile); err != nil {
			log.Error(err)
			exit.Return(1)
		}
		log.Infof("v3 is enabled: loaded schema from file: %v", *schemaFile)
	} else {
		ctx := context.Background()
		schemaJSON, err := ts.GetVSchema(ctx)
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		schema, err = planbuilder.NewSchema([]byte(schemaJSON))
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		log.Infof("v3 is enabled: loaded schema from topo")
	}

startServer:
	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	// For the initial phase vtgate is exposing
	// topoReader api. This will be subsumed by
	// vtgate once vtgate's client functions become active.
	topoReader = NewTopoReader(resilientSrvTopoServer)
	servenv.Register("toporeader", topoReader)

	healthCheck = discovery.NewHealthCheck(*connTimeoutTotal, *healthCheckRetryDelay)

	vtgate.Init(healthCheck, ts, resilientSrvTopoServer, schema, *cell, *retryDelay, *retryCount, *connTimeoutTotal, *connTimeoutPerConn, *connLife, *maxInFlight, *testGateway)
	servenv.RunDefault()
}

func newBinlogPlayerController(ts topo.Server, vtClientFactory func() binlogplayer.VtClient, mysqld mysqlctl.MysqlDaemon, cell string, keyRange *topodatapb.KeyRange, sourceShard *topodatapb.Shard_SourceShard, dbName string) *BinlogPlayerController {
	blc := &BinlogPlayerController{
		ts:                ts,
		vtClientFactory:   vtClientFactory,
		mysqld:            mysqld,
		cell:              cell,
		keyRange:          keyRange,
		dbName:            dbName,
		sourceShard:       sourceShard,
		binlogPlayerStats: binlogplayer.NewStats(),
		healthCheck:       discovery.NewHealthCheck(*binlogplayer.BinlogPlayerConnTimeout, *retryDelay, *healthCheckTimeout),
	}
	blc.shardReplicationWatcher = discovery.NewShardReplicationWatcher(ts, blc.healthCheck, cell, sourceShard.Keyspace, sourceShard.Shard, *healthCheckTopologyRefresh, 5)
	return blc
}

func newClient(master *master, replica *replica) *client {
	t, err := throttler.NewThrottler("client", "TPS", 1, throttler.MaxRateModuleDisabled, 5 /* seconds */)
	if err != nil {
		log.Fatal(err)
	}

	healthCheck := discovery.NewHealthCheck(1*time.Minute, 5*time.Second, 1*time.Minute)
	c := &client{
		master:      master,
		healthCheck: healthCheck,
		throttler:   t,
		stopChan:    make(chan struct{}),
	}
	c.healthCheck.SetListener(c, false /* sendDownEvents */)
	c.healthCheck.AddTablet(replica.fakeTablet.Tablet, "name")
	return c
}

func newBinlogPlayerController(ts topo.Server, vtClientFactory func() binlogplayer.VtClient, mysqld mysqlctl.MysqlDaemon, cell string, keyspaceIDType pb.KeyspaceIdType, keyRange *pb.KeyRange, sourceShard *pb.Shard_SourceShard, dbName string) *BinlogPlayerController {
	blc := &BinlogPlayerController{
		ts:                   ts,
		vtClientFactory:      vtClientFactory,
		mysqld:               mysqld,
		cell:                 cell,
		keyspaceIDType:       keyspaceIDType,
		keyRange:             keyRange,
		dbName:               dbName,
		sourceShard:          sourceShard,
		binlogPlayerStats:    binlogplayer.NewBinlogPlayerStats(),
		healthCheck:          discovery.NewHealthCheck(*binlogplayer.BinlogPlayerConnTimeout, *retryDelay),
		initialEndpointFound: make(chan struct{}),
	}
	blc.healthCheck.SetListener(blc)
	blc.shardReplicationWatcher = discovery.NewShardReplicationWatcher(ts, blc.healthCheck, cell, sourceShard.Keyspace, sourceShard.Shard, *healthcheckTopologyRefresh, 5)
	return blc
}

// FindHealthyRdonlyTablet returns a random healthy RDONLY tablet.
// Since we don't want to use them all, we require at least
// minHealthyRdonlyTablets servers to be healthy.
// May block up to -wait_for_healthy_rdonly_tablets_timeout.
func FindHealthyRdonlyTablet(ctx context.Context, wr *wrangler.Wrangler, healthCheck discovery.HealthCheck, cell, keyspace, shard string, minHealthyRdonlyTablets int) (*topodatapb.TabletAlias, error) {
	if healthCheck == nil {
		// No healthcheck instance provided. Create one.
		healthCheck = discovery.NewHealthCheck(*remoteActionsTimeout, *healthcheckRetryDelay, *healthCheckTimeout)
		watcher := discovery.NewShardReplicationWatcher(wr.TopoServer(), healthCheck, cell, keyspace, shard, *healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
		defer watcher.Stop()
		defer healthCheck.Close()
	}

	healthyTablets, err := waitForHealthyRdonlyTablets(ctx, wr, healthCheck, cell, keyspace, shard, minHealthyRdonlyTablets, *waitForHealthyTabletsTimeout)
	if err != nil {
		return nil, err
	}

	// random server in the list is what we want
	index := rand.Intn(len(healthyTablets))
	return healthyTablets[index].Tablet.Alias, nil
}

// newBinlogPlayerController instantiates a new BinlogPlayerController.
// Use Start() and Stop() to start and stop it.
// Once stopped, you should call Close() to stop and free resources e.g. the
// healthcheck instance.
func newBinlogPlayerController(ts topo.Server, vtClientFactory func() binlogplayer.VtClient, mysqld mysqlctl.MysqlDaemon, cell string, keyRange *topodatapb.KeyRange, sourceShard *topodatapb.Shard_SourceShard, dbName string) *BinlogPlayerController {
	healthCheck := discovery.NewHealthCheck(*binlogplayer.BinlogPlayerConnTimeout, *healthcheckRetryDelay, *healthCheckTimeout)
	return &BinlogPlayerController{
		ts:                ts,
		vtClientFactory:   vtClientFactory,
		mysqld:            mysqld,
		cell:              cell,
		keyRange:          keyRange,
		dbName:            dbName,
		sourceShard:       sourceShard,
		binlogPlayerStats: binlogplayer.NewStats(),
		// Note: healthCheck and shardReplicationWatcher remain active independent
		// of whether the BinlogPlayerController is Start()'d or Stop()'d.
		// Use Close() after Stop() to finally close them and free their resources.
		healthCheck:             healthCheck,
		shardReplicationWatcher: discovery.NewShardReplicationWatcher(ts, healthCheck, cell, sourceShard.Keyspace, sourceShard.Shard, *healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency),
	}
}

func TestGRPCDiscovery(t *testing.T) {
	flag.Set("tablet_protocol", "grpc")
	flag.Set("gateway_implementation", "discoverygateway")

	// Fake services for the tablet, topo server.
	service, ts, cell := CreateFakeServers(t)

	// Listen on a random port.
	listener, err := net.Listen("tcp", ":0")
	if err != nil {
		t.Fatalf("Cannot listen: %v", err)
	}
	host := listener.Addr().(*net.TCPAddr).IP.String()
	port := listener.Addr().(*net.TCPAddr).Port

	// Create a gRPC server and listen on the port.
	server := grpc.NewServer()
	grpcqueryservice.RegisterForTest(server, service)
	go server.Serve(listener)

	// Create the discovery healthcheck, and the gateway.
	// Wait for the right tablets to be present.
	hc := discovery.NewHealthCheck(30*time.Second, 10*time.Second, 2*time.Minute)
	hc.AddTablet(cell, "test_tablet", &topodatapb.Tablet{
		Alias: &topodatapb.TabletAlias{
			Cell: cell,
		},
		Keyspace: tabletconntest.TestTarget.Keyspace,
		Shard:    tabletconntest.TestTarget.Shard,
		Type:     tabletconntest.TestTarget.TabletType,
		Hostname: host,
		PortMap: map[string]int32{
			"grpc": int32(port),
		},
	})
	dg := gateway.GetCreator()(hc, ts, ts, cell, 2, []topodatapb.TabletType{tabletconntest.TestTarget.TabletType})

	// and run the test suite.
	TestSuite(t, "discovery-grpc", dg, service)
}

// findTargets phase:
// - find one rdonly in the source shard
// - mark it as 'worker' pointing back to us
// - get the aliases of all the targets
func (vscw *VerticalSplitCloneWorker) findTargets(ctx context.Context) error {
	vscw.setState(WorkerStateFindTargets)

	// find an appropriate tablet in the source shard
	var err error
	vscw.sourceAlias, err = FindWorkerTablet(ctx, vscw.wr, vscw.cleaner, nil /* tsc */, vscw.cell, vscw.sourceKeyspace, "0", vscw.minHealthyRdonlyTablets)
	if err != nil {
		return fmt.Errorf("FindWorkerTablet() failed for %v/%v/0: %v", vscw.cell, vscw.sourceKeyspace, err)
	}
	vscw.wr.Logger().Infof("Using tablet %v as the source", topoproto.TabletAliasString(vscw.sourceAlias))

	// get the tablet info for it
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	ti, err := vscw.wr.TopoServer().GetTablet(shortCtx, vscw.sourceAlias)
	cancel()
	if err != nil {
		return fmt.Errorf("cannot read tablet %v: %v", topoproto.TabletAliasString(vscw.sourceAlias), err)
	}
	vscw.sourceTablet = ti.Tablet

	// stop replication on it
	shortCtx, cancel = context.WithTimeout(ctx, *remoteActionsTimeout)
	err = vscw.wr.TabletManagerClient().StopSlave(shortCtx, vscw.sourceTablet)
	cancel()
	if err != nil {
		return fmt.Errorf("cannot stop replication on tablet %v", topoproto.TabletAliasString(vscw.sourceAlias))
	}

	wrangler.RecordStartSlaveAction(vscw.cleaner, vscw.sourceTablet)

	// Initialize healthcheck and add destination shards to it.
	vscw.healthCheck = discovery.NewHealthCheck(*remoteActionsTimeout, *healthcheckRetryDelay, *healthCheckTimeout)
	vscw.tsc = discovery.NewTabletStatsCache(vscw.healthCheck, vscw.cell)
	watcher := discovery.NewShardReplicationWatcher(vscw.wr.TopoServer(), vscw.healthCheck,
		vscw.cell, vscw.destinationKeyspace, vscw.destinationShard,
		*healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
	vscw.destinationShardWatchers = append(vscw.destinationShardWatchers, watcher)

	// Make sure we find a master for each destination shard and log it.
	vscw.wr.Logger().Infof("Finding a MASTER tablet for each destination shard...")
	waitCtx, waitCancel := context.WithTimeout(ctx, *waitForHealthyTabletsTimeout)
	defer waitCancel()
	if err := vscw.tsc.WaitForTablets(waitCtx, vscw.cell, vscw.destinationKeyspace, vscw.destinationShard, []topodatapb.TabletType{topodatapb.TabletType_MASTER}); err != nil {
		return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v): %v", vscw.destinationKeyspace, vscw.destinationShard, vscw.cell, err)
	}
	masters := vscw.tsc.GetHealthyTabletStats(vscw.destinationKeyspace, vscw.destinationShard, topodatapb.TabletType_MASTER)
	if len(masters) == 0 {
		return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v) in HealthCheck: empty TabletStats list", vscw.destinationKeyspace, vscw.destinationShard, vscw.cell)
	}
	master := masters[0]

	// Get the MySQL database name of the tablet.
	keyspaceAndShard := topoproto.KeyspaceShardString(vscw.destinationKeyspace, vscw.destinationShard)
	vscw.destinationDbNames[keyspaceAndShard] = topoproto.TabletDbName(master.Tablet)

	// TODO(mberlin): Verify on the destination master that the
	// _vt.blp_checkpoint table has the latest schema.

	vscw.wr.Logger().Infof("Using tablet %v as destination master for %v/%v", topoproto.TabletAliasString(master.Tablet.Alias), vscw.destinationKeyspace, vscw.destinationShard)
	vscw.wr.Logger().Infof("NOTE: The used master of a destination shard might change over the course of the copy e.g. due to a reparent. The HealthCheck module will track and log master changes and any error message will always refer the actually used master address.")

	return nil
}

func (wr *Wrangler) waitForDrainInCell(ctx context.Context, cell, keyspace, shard string, servedType topodatapb.TabletType,
	retryDelay, healthCheckTopologyRefresh, healthcheckRetryDelay, healthCheckTimeout time.Duration) error {
	hc := discovery.NewHealthCheck(healthCheckTimeout /* connectTimeout */, healthcheckRetryDelay, healthCheckTimeout, cell)
	defer hc.Close()
	watcher := discovery.NewShardReplicationWatcher(wr.TopoServer(), hc, cell, keyspace, shard, healthCheckTopologyRefresh, 5 /* topoReadConcurrency */)
	defer watcher.Stop()

	if err := discovery.WaitForEndPoints(ctx, hc, cell, keyspace, shard, []topodatapb.TabletType{servedType}); err != nil {
		return fmt.Errorf("%v: error waiting for initial %v endpoints for %v/%v: %v", cell, servedType, keyspace, shard, err)
	}

	wr.Logger().Infof("%v: Waiting for %.1f seconds to make sure that the discovery module retrieves healthcheck information from all tablets.",
		cell, healthCheckTimeout.Seconds())
	// Wait at least for -vtctl_healthcheck_timeout to elapse to make sure that we
	// see all healthy tablets. Otherwise, we might miss some tablets.
	// It's safe to wait not longer for this because we would only miss slow
	// tablets and vtgate would not serve from such tablets anyway.
	time.Sleep(healthCheckTimeout)

	// Now check the QPS rate of all tablets until the timeout expires.
	startTime := time.Now()
	for {
		healthyTabletsCount := 0
		// map key: tablet uid
		drainedHealthyTablets := make(map[uint32]*discovery.EndPointStats)
		notDrainedHealtyTablets := make(map[uint32]*discovery.EndPointStats)

		addrs := hc.GetEndPointStatsFromTarget(keyspace, shard, servedType)
		healthyTabletsCount = 0
		for _, addr := range addrs {
			// TODO(mberlin): Move this health check logic into a common function
			// because other code uses it as well e.g. go/vt/worker/topo_utils.go.
			if addr.Stats == nil || addr.Stats.HealthError != "" || addr.Stats.SecondsBehindMaster > 30 {
				// not healthy
				continue
			}

			healthyTabletsCount++
			if addr.Stats.Qps == 0.0 {
				drainedHealthyTablets[addr.EndPoint.Uid] = addr
			} else {
				notDrainedHealtyTablets[addr.EndPoint.Uid] = addr
			}
		}

		if len(drainedHealthyTablets) == healthyTabletsCount {
			wr.Logger().Infof("%v: All %d healthy tablets were drained after %.1f seconds (not counting %.1f seconds for the initial wait).",
				cell, healthyTabletsCount, time.Now().Sub(startTime).Seconds(), healthCheckTimeout.Seconds())
			break
		}

		// Continue waiting, sleep in between.
		deadlineString := ""
		if d, ok := ctx.Deadline(); ok {
			deadlineString = fmt.Sprintf(" up to %.1f more seconds", d.Sub(time.Now()).Seconds())
		}
		wr.Logger().Infof("%v: Waiting%v for all healthy tablets to be drained (%d/%d done).",
			cell, deadlineString, len(drainedHealthyTablets), healthyTabletsCount)

		timer := time.NewTimer(retryDelay)
		select {
		case <-ctx.Done():
			timer.Stop()

			var l []string
			for _, eps := range notDrainedHealtyTablets {
				l = append(l, formatEndpointStats(eps))
			}
			return fmt.Errorf("%v: WaitForDrain failed for %v tablets in %v/%v. Only %d/%d tablets were drained. err: %v List of tablets which were not drained:\n%v",
				cell, servedType, keyspace, shard, len(drainedHealthyTablets), healthyTabletsCount, ctx.Err(), strings.Join(l, "\n"))
		case <-timer.C:
		}
	}

	return nil
}

func main() {
	defer exit.Recover()

	// flag parsing
	flags := dbconfigs.AppConfig | dbconfigs.AllPrivsConfig | dbconfigs.DbaConfig |
		dbconfigs.FilteredConfig | dbconfigs.ReplConfig
	dbconfigs.RegisterFlags(flags)
	mysqlctl.RegisterFlags()
	flag.Parse()
	if len(flag.Args()) > 0 {
		flag.Usage()
		log.Errorf("vtcombo doesn't take any positional arguments")
		exit.Return(1)
	}

	// parse the input topology
	tpb := &vttestpb.VTTestTopology{}
	if err := proto.UnmarshalText(*protoTopo, tpb); err != nil {
		log.Errorf("cannot parse topology: %v", err)
		exit.Return(1)
	}

	// default cell to "test" if unspecified
	if len(tpb.Cells) == 0 {
		tpb.Cells = append(tpb.Cells, "test")
	}

	// set discoverygateway flag to default value
	flag.Set("cells_to_watch", strings.Join(tpb.Cells, ","))

	// vtctld UI requires the cell flag
	flag.Set("cell", tpb.Cells[0])
	flag.Set("enable_realtime_stats", "true")
	flag.Set("log_dir", "$VTDATAROOT/tmp")

	// create zk client config file
	config := path.Join(os.Getenv("VTDATAROOT"), "vt_0000000001/tmp/test-zk-client-conf.json")
	cellmap := make(map[string]string)
	for _, cell := range tpb.Cells {
		cellmap[cell] = "localhost"
	}
	b, err := json.Marshal(cellmap)
	if err != nil {
		log.Errorf("failed to marshal json: %v", err)
	}

	f, err := os.Create(config)
	if err != nil {
		log.Errorf("failed to create zk config file: %v", err)
	}
	defer f.Close()
	_, err = f.WriteString(string(b[:]))
	if err != nil {
		log.Errorf("failed to write to zk config file: %v", err)
	}
	os.Setenv("ZK_CLIENT_CONFIG", config)

	// register topo server
	zkconn := fakezk.NewConn()
	topo.RegisterServer("fakezk", zktopo.NewServer(zkconn))
	ts = topo.GetServerByName("fakezk")

	servenv.Init()
	tabletserver.Init()

	// database configs
	mycnf, err := mysqlctl.NewMycnfFromFlags(0)
	if err != nil {
		log.Errorf("mycnf read failed: %v", err)
		exit.Return(1)
	}
	dbcfgs, err := dbconfigs.Init(mycnf.SocketFile, flags)
	if err != nil {
		log.Warning(err)
	}
	mysqld := mysqlctl.NewMysqld(mycnf, &dbcfgs.Dba, &dbcfgs.AllPrivs, &dbcfgs.App, &dbcfgs.Repl, true /* enablePublishStats */)
	servenv.OnClose(mysqld.Close)

	// tablets configuration and init
	if err := initTabletMap(ts, tpb, mysqld, dbcfgs, *schemaDir, mycnf); err != nil {
		log.Errorf("initTabletMapProto failed: %v", err)
		exit.Return(1)
	}

	// vtgate configuration and init
	resilientSrvTopoServer := vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")
	healthCheck := discovery.NewHealthCheck(30*time.Second /*connTimeoutTotal*/, 1*time.Millisecond /*retryDelay*/, 1*time.Hour /*healthCheckTimeout*/)
	tabletTypesToWait := []topodatapb.TabletType{
		topodatapb.TabletType_MASTER,
		topodatapb.TabletType_REPLICA,
		topodatapb.TabletType_RDONLY,
	}
	vtgate.Init(context.Background(), healthCheck, ts, resilientSrvTopoServer, tpb.Cells[0], 2 /*retryCount*/, tabletTypesToWait)

	// vtctld configuration and init
	vtctld.InitVtctld(ts)
	vtctld.HandleExplorer("zk", zktopo.NewZkExplorer(zkconn))

	servenv.OnTerm(func() {
		// FIXME(alainjobart): stop vtgate
//.........这里部分代码省略.........

func main() {
	defer exit.Recover()

	// flag parsing
	flags := dbconfigs.AppConfig | dbconfigs.DbaConfig |
		dbconfigs.FilteredConfig | dbconfigs.ReplConfig
	dbconfigs.RegisterFlags(flags)
	mysqlctl.RegisterFlags()
	flag.Parse()
	if len(flag.Args()) > 0 {
		flag.Usage()
		log.Errorf("vtcombo doesn't take any positional arguments")
		exit.Return(1)
	}

	// register topo server
	zkconn := fakezk.NewConn()
	topo.RegisterServer("fakezk", zktopo.NewServer(zkconn))
	ts = topo.GetServerByName("fakezk")

	servenv.Init()
	tabletserver.Init()

	// database configs
	mycnf, err := mysqlctl.NewMycnfFromFlags(0)
	if err != nil {
		log.Errorf("mycnf read failed: %v", err)
		exit.Return(1)
	}
	dbcfgs, err := dbconfigs.Init(mycnf.SocketFile, flags)
	if err != nil {
		log.Warning(err)
	}
	mysqld := mysqlctl.NewMysqld("Dba", "App", mycnf, &dbcfgs.Dba, &dbcfgs.App.ConnParams, &dbcfgs.Repl)
	servenv.OnClose(mysqld.Close)

	// tablets configuration and init
	initTabletMap(ts, *topology, mysqld, dbcfgs, mycnf)

	// vschema
	var schema *planbuilder.Schema
	if *vschema != "" {
		schema, err = planbuilder.LoadFile(*vschema)
		if err != nil {
			log.Error(err)
			exit.Return(1)
		}
		log.Infof("v3 is enabled: loaded schema from file")
	}

	// vtgate configuration and init
	resilientSrvTopoServer := vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")
	healthCheck := discovery.NewHealthCheck(30*time.Second /*connTimeoutTotal*/, 1*time.Millisecond /*retryDelay*/, 1*time.Minute /*healthCheckTimeout*/)
	tabletTypesToWait := []topodatapb.TabletType{
		topodatapb.TabletType_MASTER,
		topodatapb.TabletType_REPLICA,
		topodatapb.TabletType_RDONLY,
	}
	vtgate.Init(healthCheck, ts, resilientSrvTopoServer, schema, cell, 1*time.Millisecond /*retryDelay*/, 2 /*retryCount*/, 30*time.Second /*connTimeoutTotal*/, 10*time.Second /*connTimeoutPerConn*/, 365*24*time.Hour /*connLife*/, tabletTypesToWait, 0 /*maxInFlight*/, "" /*testGateway*/)

	// vtctld configuration and init
	vtctld.InitVtctld(ts)
	vtctld.HandleExplorer("zk", zktopo.NewZkExplorer(zkconn))

	servenv.OnTerm(func() {
		// FIXME(alainjobart): stop vtgate
	})
	servenv.OnClose(func() {
		log.Infof("Total count of new connections to MySQL: %v", expvar.Get("mysql-new-connection-count"))
		// We will still use the topo server during lameduck period
		// to update our state, so closing it in OnClose()
		topo.CloseServers()
	})
	servenv.RunDefault()
}