xds/server: create the xDS client when the xDS enabled gRPC server is created

examples/features/xds/server/main.go

@@ -85,7 +85,10 @@ func main() {
 		}
 	}
 
-	greeterServer := xds.NewGRPCServer(grpc.Creds(creds))
+	greeterServer, err := xds.NewGRPCServer(grpc.Creds(creds))
+	if err != nil {
+		log.Fatalf("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	pb.RegisterGreeterServer(greeterServer, &server{serverName: determineHostname()})
 
 	healthPort := fmt.Sprintf(":%d", *port+1)

internal/testutils/xds/e2e/setup_management_server.go

@@ -20,6 +20,7 @@ package e2e
 
 import (
 	"encoding/json"
+	"fmt"
 	"path"
 	"testing"
 
@@ -55,18 +56,39 @@ func SetupManagementServer(t *testing.T, opts ManagementServerOptions) (*Managem
 		}
 	}()
 
-	// Create a directory to hold certs and key files used on the server side.
-	serverDir, err := createTmpDirWithFiles("testServerSideXDS*", "x509/server1_cert.pem", "x509/server1_key.pem", "x509/client_ca_cert.pem")
+	nodeID := uuid.New().String()
+	bootstrapContents, err := DefaultBootstrapContents(nodeID, server.Address)
 	if err != nil {
 		server.Stop()
 		t.Fatal(err)
 	}
+	var rb resolver.Builder
+	if newResolver := internal.NewXDSResolverWithConfigForTesting; newResolver != nil {
+		rb, err = newResolver.(func([]byte) (resolver.Builder, error))(bootstrapContents)
+		if err != nil {
+			server.Stop()
+			t.Fatalf("Failed to create xDS resolver for testing: %v", err)
+		}
+	}
+
+	return server, nodeID, bootstrapContents, rb, func() { server.Stop() }
+}
+
+// DefaultBootstrapContents creates a default bootstrap configuration with the
+// given node ID and server URI. It also creates certificate provider
+// configuration and sets the listener resource name template to be used on the
+// server side.
+func DefaultBootstrapContents(nodeID, serverURI string) ([]byte, error) {
+	// Create a directory to hold certs and key files used on the server side.
+	serverDir, err := createTmpDirWithFiles("testServerSideXDS*", "x509/server1_cert.pem", "x509/server1_key.pem", "x509/client_ca_cert.pem")
+	if err != nil {
+		return nil, fmt.Errorf("failed to create bootstrap configuration: %v", err)
+	}
 
 	// Create a directory to hold certs and key files used on the client side.
 	clientDir, err := createTmpDirWithFiles("testClientSideXDS*", "x509/client1_cert.pem", "x509/client1_key.pem", "x509/server_ca_cert.pem")
 	if err != nil {
-		server.Stop()
-		t.Fatal(err)
+		return nil, fmt.Errorf("failed to create bootstrap configuration: %v", err)
 	}
 
 	// Create certificate providers section of the bootstrap config with entries
@@ -76,27 +98,15 @@ func SetupManagementServer(t *testing.T, opts ManagementServerOptions) (*Managem
 		ClientSideCertProviderInstance: DefaultFileWatcherConfig(path.Join(clientDir, certFile), path.Join(clientDir, keyFile), path.Join(clientDir, rootFile)),
 	}
 
-	// Create a bootstrap file in a temporary directory.
-	nodeID := uuid.New().String()
-	bootstrapContents, err := bootstrap.Contents(bootstrap.Options{
+	// Create the bootstrap configuration.
+	bs, err := bootstrap.Contents(bootstrap.Options{
 		NodeID:                             nodeID,
-		ServerURI:                          server.Address,
+		ServerURI:                          serverURI,
 		CertificateProviders:               cpc,
 		ServerListenerResourceNameTemplate: ServerListenerResourceNameTemplate,
 	})
 	if err != nil {
-		server.Stop()
-		t.Fatalf("Failed to create bootstrap file: %v", err)
+		return nil, fmt.Errorf("failed to create bootstrap configuration: %v", err)
 	}
-
-	var rb resolver.Builder
-	if newResolver := internal.NewXDSResolverWithConfigForTesting; newResolver != nil {
-		rb, err = newResolver.(func([]byte) (resolver.Builder, error))(bootstrapContents)
-		if err != nil {
-			server.Stop()
-			t.Fatalf("Failed to create xDS resolver for testing: %v", err)
-		}
-	}
-
-	return server, nodeID, bootstrapContents, rb, func() { server.Stop() }
+	return bs, nil
 }

interop/xds/server/server.go

@@ -156,7 +156,10 @@ func main() {
 
 	// Create an xDS enabled gRPC server, register the test service
 	// implementation and start serving.
-	testServer := xds.NewGRPCServer(grpc.Creds(creds), xds.ServingModeCallback(xdsServingModeCallback))
+	testServer, err := xds.NewGRPCServer(grpc.Creds(creds), xds.ServingModeCallback(xdsServingModeCallback))
+	if err != nil {
+		logger.Fatal("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	testgrpc.RegisterTestServiceServer(testServer, testService)
 	go func() {
 		if err := testServer.Serve(testLis); err != nil {

test/xds/xds_client_ignore_resource_deletion_test.go

@@ -306,7 +306,10 @@ func setupGRPCServerWithModeChangeChannelAndServe(t *testing.T, bootstrapContent
 		t.Logf("Serving mode for listener %q changed to %q, err: %v", addr.String(), args.Mode, args.Err)
 		updateCh <- args.Mode
 	})
-	server := xds.NewGRPCServer(grpc.Creds(insecure.NewCredentials()), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	server, err := xds.NewGRPCServer(grpc.Creds(insecure.NewCredentials()), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	if err != nil {
+		t.Fatalf("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	t.Cleanup(server.Stop)
 	testgrpc.RegisterTestServiceServer(server, &testService{})
 

test/xds/xds_server_integration_test.go

@@ -82,7 +82,10 @@ func setupGRPCServer(t *testing.T, bootstrapContents []byte) (net.Listener, func
 	})
 
 	// Initialize an xDS-enabled gRPC server and register the stubServer on it.
-	server := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	server, err := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	if err != nil {
+		t.Fatalf("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	testgrpc.RegisterTestServiceServer(server, &testService{})
 
 	// Create a local listener and pass it to Serve().

test/xds/xds_server_serving_mode_test.go

@@ -63,7 +63,10 @@ func (s) TestServerSideXDS_RedundantUpdateSuppression(t *testing.T) {
 	})
 
 	// Initialize an xDS-enabled gRPC server and register the stubServer on it.
-	server := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	server, err := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	if err != nil {
+		t.Fatalf("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	defer server.Stop()
 	testgrpc.RegisterTestServiceServer(server, &testService{})
 
@@ -205,7 +208,10 @@ func (s) TestServerSideXDS_ServingModeChanges(t *testing.T) {
 	})
 
 	// Initialize an xDS-enabled gRPC server and register the stubServer on it.
-	server := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	server, err := xds.NewGRPCServer(grpc.Creds(creds), modeChangeOpt, xds.BootstrapContentsForTesting(bootstrapContents))
+	if err != nil {
+		t.Fatalf("Failed to create an xDS enabled gRPC server: %v", err)
+	}
 	defer server.Stop()
 	testgrpc.RegisterTestServiceServer(server, &testService{})
 

xds/server.go

@@ -23,7 +23,6 @@ import (
 	"errors"
 	"fmt"
 	"net"
-	"sync"
 
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
@@ -76,24 +75,19 @@ type grpcServer interface {
 // grpc.ServiceRegistrar interface and can be passed to service registration
 // functions in IDL generated code.
 type GRPCServer struct {
-	gs            grpcServer
-	quit          *grpcsync.Event
-	logger        *internalgrpclog.PrefixLogger
-	xdsCredsInUse bool
-	opts          *serverOptions
-
-	// clientMu is used only in initXDSClient(), which is called at the
-	// beginning of Serve(), where we have to decide if we have to create a
-	// client or use an existing one.
-	clientMu       sync.Mutex
+	gs             grpcServer
+	quit           *grpcsync.Event
+	logger         *internalgrpclog.PrefixLogger
+	xdsCredsInUse  bool
+	opts           *serverOptions
 	xdsC           xdsclient.XDSClient
 	xdsClientClose func()
 }
 
 // NewGRPCServer creates an xDS-enabled gRPC server using the passed in opts.
 // The underlying gRPC server has no service registered and has not started to
 // accept requests yet.
-func NewGRPCServer(opts ...grpc.ServerOption) *GRPCServer {
+func NewGRPCServer(opts ...grpc.ServerOption) (*GRPCServer, error) {
 	newOpts := []grpc.ServerOption{
 		grpc.ChainUnaryInterceptor(xdsUnaryInterceptor),
 		grpc.ChainStreamInterceptor(xdsStreamInterceptor),
@@ -103,8 +97,6 @@ func NewGRPCServer(opts ...grpc.ServerOption) *GRPCServer {
 		gs:   newGRPCServer(newOpts...),
 		quit: grpcsync.NewEvent(),
 	}
-	s.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf(serverPrefix, s))
-	s.logger.Infof("Created xds.GRPCServer")
 	s.handleServerOptions(opts)
 
 	// We type assert our underlying gRPC server to the real grpc.Server here
@@ -119,8 +111,48 @@ func NewGRPCServer(opts ...grpc.ServerOption) *GRPCServer {
 		}
 	}
 
+	// Initializing the xDS client upfront (instead of at serving time)
+	// simplifies the code by eliminating the need for a mutex to protect the
+	// xdsC and xdsClientClose fields.
+	newXDSClient := newXDSClient
+	if s.opts.bootstrapContentsForTesting != nil {
+		// Bootstrap file contents may be specified as a server option for tests.
+		newXDSClient = func() (xdsclient.XDSClient, func(), error) {
+			return xdsclient.NewWithBootstrapContentsForTesting(s.opts.bootstrapContentsForTesting)
+		}
+	}
+	xdsClient, xdsClientClose, err := newXDSClient()
+	if err != nil {
+		return nil, fmt.Errorf("xDS client creation failed: %v", err)
+	}
+
+	// Validate the bootstrap configuration for server specific fields.
+
+	// Listener resource name template is mandatory on the server side.
+	cfg := xdsClient.BootstrapConfig()
+	if cfg.ServerListenerResourceNameTemplate == "" {
+		xdsClientClose()
+		return nil, errors.New("missing server_listener_resource_name_template in the bootstrap configuration")
+	}
+
+	// If xds credentials were specified by the user, but bootstrap configs do
+	// not contain any certificate provider configuration, it is better to fail
+	// right now rather than failing when attempting to create certificate
+	// providers after receiving an LDS response with security configuration.
+	if s.xdsCredsInUse {
+		if len(cfg.CertProviderConfigs) == 0 {
+			xdsClientClose()
+			return nil, fmt.Errorf("xds credentials are passed to the user, but certificate_providers config is missing in the bootstrap configuration")
+		}
+	}
+	s.xdsC = xdsClient
+	s.xdsClientClose = xdsClientClose
+
+	s.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf(serverPrefix, s))
+	s.logger.Infof("Created xds.GRPCServer")
 	s.logger.Infof("xDS credentials in use: %v", s.xdsCredsInUse)
-	return s
+
+	return s, nil
 }
 
 // handleServerOptions iterates through the list of server options passed in by
@@ -169,35 +201,6 @@ func (s *GRPCServer) GetServiceInfo() map[string]grpc.ServiceInfo {
 	return s.gs.GetServiceInfo()
 }
 
-// initXDSClient creates a new xdsClient if there is no existing one available.
-func (s *GRPCServer) initXDSClient() error {
-	s.clientMu.Lock()
-	defer s.clientMu.Unlock()
-	if s.quit.HasFired() {
-		return grpc.ErrServerStopped
-	}
-
-	if s.xdsC != nil {
-		return nil
-	}
-
-	newXDSClient := newXDSClient
-	if s.opts.bootstrapContentsForTesting != nil {
-		// Bootstrap file contents may be specified as a server option for tests.
-		newXDSClient = func() (xdsclient.XDSClient, func(), error) {
-			return xdsclient.NewWithBootstrapContentsForTesting(s.opts.bootstrapContentsForTesting)
-		}
-	}
-
-	client, close, err := newXDSClient()
-	if err != nil {
-		return fmt.Errorf("xds: failed to create xds-client: %v", err)
-	}
-	s.xdsC = client
-	s.xdsClientClose = close
-	return nil
-}
-
 // Serve gets the underlying gRPC server to accept incoming connections on the
 // listener lis, which is expected to be listening on a TCP port.
 //
@@ -211,35 +214,16 @@ func (s *GRPCServer) Serve(lis net.Listener) error {
 		return fmt.Errorf("xds: GRPCServer expects listener to return a net.TCPAddr. Got %T", lis.Addr())
 	}
 
-	// If this is the first time Serve() is being called, we need to initialize
-	// our xdsClient. If not, we can use the existing one.
-	if err := s.initXDSClient(); err != nil {
-		return err
-	}
-	cfg := s.xdsC.BootstrapConfig()
-	if cfg == nil {
-		return errors.New("bootstrap configuration is empty")
-	}
-
-	// If xds credentials were specified by the user, but bootstrap configs do
-	// not contain any certificate provider configuration, it is better to fail
-	// right now rather than failing when attempting to create certificate
-	// providers after receiving an LDS response with security configuration.
-	if s.xdsCredsInUse {
-		if len(cfg.CertProviderConfigs) == 0 {
-			return errors.New("xds: certificate_providers config missing in bootstrap file")
-		}
+	if s.quit.HasFired() {
+		return grpc.ErrServerStopped
 	}
 
 	// The server listener resource name template from the bootstrap
 	// configuration contains a template for the name of the Listener resource
 	// to subscribe to for a gRPC server. If the token `%s` is present in the
 	// string, it will be replaced with the server's listening "IP:port" (e.g.,
-	// "0.0.0.0:8080", "[::]:8080"). The absence of a template will be treated
-	// as an error since we do not have any default value for this.
-	if cfg.ServerListenerResourceNameTemplate == "" {
-		return errors.New("missing server_listener_resource_name_template in the bootstrap configuration")
-	}
+	// "0.0.0.0:8080", "[::]:8080").
+	cfg := s.xdsC.BootstrapConfig()
 	name := bootstrap.PopulateResourceTemplate(cfg.ServerListenerResourceNameTemplate, lis.Addr().String())
 
 	modeUpdateCh := buffer.NewUnbounded()
@@ -335,8 +319,6 @@ func (s *GRPCServer) handleServingModeChanges(updateCh *buffer.Unbounded) {
 // corresponding pending RPCs on the client side will get notified by connection
 // errors.
 func (s *GRPCServer) Stop() {
-	s.clientMu.Lock()
-	defer s.clientMu.Unlock()
 	s.quit.Fire()
 	s.gs.Stop()
 	if s.xdsC != nil {
@@ -348,8 +330,6 @@ func (s *GRPCServer) Stop() {
 // from accepting new connections and RPCs and blocks until all the pending RPCs
 // are finished.
 func (s *GRPCServer) GracefulStop() {
-	s.clientMu.Lock()
-	defer s.clientMu.Unlock()
 	s.quit.Fire()
 	s.gs.GracefulStop()
 	if s.xdsC != nil {