grpc: disable and document overrides of OS default TCP keepalive by Go

dialoptions.go

@@ -413,6 +413,9 @@ func WithTimeout(d time.Duration) DialOption {
 // connections. If FailOnNonTempDialError() is set to true, and an error is
 // returned by f, gRPC checks the error's Temporary() method to decide if it
 // should try to reconnect to the network address.
+//
+// Note: Go overrides the OS defaults for TCP keepalive interval to 15s.
+// To retain the OS defaults, pass in a custom dialer with KeepAlive set to a negative duration.
 func WithContextDialer(f func(context.Context, string) (net.Conn, error)) DialOption {
 	return newFuncDialOption(func(o *dialOptions) {
 		o.copts.Dialer = f

examples/helloworld/greeter_server/main.go

@@ -25,6 +25,7 @@ import (
 	"fmt"
 	"log"
 	"net"
+	"time"
 
 	"google.golang.org/grpc"
 	pb "google.golang.org/grpc/examples/helloworld/helloworld"
@@ -47,7 +48,11 @@ func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloRe
 
 func main() {
 	flag.Parse()
-	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	// ListenConfig allows options to be passed to the listener.
+	var lc net.ListenConfig
+	// Setting KeepAlive to -1 allows the listener to retain OS default TCP keep-alive interval.
+	lc.KeepAlive = time.Duration(-1)
+	lis, err := lc.Listen(context.Background(), "tcp", fmt.Sprintf(":%d", *port))
 	if err != nil {
 		log.Fatalf("failed to listen: %v", err)
 	}

internal/transport/http2_client.go

@@ -176,7 +176,7 @@ func dial(ctx context.Context, fn func(context.Context, string) (net.Conn, error
 	if networkType == "tcp" && useProxy {
 		return proxyDial(ctx, address, grpcUA)
 	}
-	return (&net.Dialer{}).DialContext(ctx, networkType, address)
+	return (&net.Dialer{KeepAlive: time.Duration(-1)}).DialContext(ctx, networkType, address)
 }
 
 func isTemporary(err error) bool {

server.go

@@ -813,6 +813,12 @@ func (l *listenSocket) Close() error {
 // Serve returns when lis.Accept fails with fatal errors.  lis will be closed when
 // this method returns.
 // Serve will return a non-nil error unless Stop or GracefulStop is called.
+//
+// Note: Go overrides the OS defaults for TCP keepalive interval to 15s.
+// To retain the OS defaults, you will need to create a net.ListenConfig with the
+// KeepAlive parameter set to a negative value and use the Listen method on it to create
+// the net.Listener to pass to this function.
+// See https://github.com/grpc/grpc-go/blob/master/examples/helloworld/greeter_client/main.go#L51
 func (s *Server) Serve(lis net.Listener) error {
 	s.mu.Lock()
 	s.printf("serving")