Why does connection to localhost fail on local ? #7429
Description
I faced this issue when I was testing out a simple application; Not able to put a finger on what exactly am missing.
My client code is returning with this error
could not greet: rpc error: code = DeadlineExceeded desc = context deadline exceededI have my server running as
const (
port = ":50051"
)
// server is used to implement helloworld.GreeterServer.
type server struct {
helloworld.UnimplementedGreeterServer
}
// SayHello implements helloworld.GreeterServer
func (s *server) SayHello(ctx context.Context, in *helloworld.HelloRequest) (*helloworld.HelloReply, error) {
log.Printf("Received: %v\n", in.GetName())
return &helloworld.HelloReply{Message: "Hello " + in.Name}, nil
}
func main() {
lis, err := net.Listen("tcp", port)
if err != nil {
log.Fatalf("failed to listen: %v", err)
}
s := grpc.NewServer()
helloworld.RegisterGreeterServer(s, &server{})
log.Printf("server starting at %v\n", lis.Addr())
if err := s.Serve(lis); err != nil {
log.Fatalf("failed to serve: %v", err)
}
}Client connecting to localhost as
const (
address = "localhost:50051"
// address = "[::1]:50051"
// address = "127.0.0.1:50051"
defaultName = "world"
)
func main() {
// Set up a connection to the server.
conn, err := grpc.NewClient(address, grpc.WithTransportCredentials(insecure.NewCredentials()))
if err != nil {
log.Fatalf("did not connect: %v", err)
}
defer conn.Close()
c := helloworld.NewGreeterClient(conn)
// Contact the server and print out its response.
name := defaultName
if len(os.Args) > 1 {
name = os.Args[1]
}
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
defer cancel()
r, err := c.SayHello(ctx, &helloworld.HelloRequest{Name: name})
if err != nil {
log.Fatalf("could not greet: %v", err)
}
log.Printf("Greeting: %s", r.GetMessage())
}This code fails.
But when I connect with either of
address = "[::1]:50051"
address = "127.0.0.1:50051"
It works. I am trying to understand what am missing here. Can anyone help me understand? TIA!
Full application code available here
UPDATE (More Info):
Some more information
Version
google.golang.org/grpc v1.65.0
I am able to connect if I am using 127.0.0.0 and [::1]
The issue specifically seems to occur when localhost is used.
etc/hosts is below
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting. Do not change this entry.
##
127.0.0.1 localhost
127.0.0.1 mail.local
255.255.255.255 broadcasthost
::1 localhost
I am running the server at add = :50051 and initialising like
lis, err := net.Listen("tcp", port)
It works with Dial
When I use Dial it works
conn, err := grpc.DialContext(ctx, addr,
grpc.WithTransportCredentials(insecure.NewCredentials()),
grpc.WithBlock(),
)I have tried all variations to connect without using Dial, and everything except localhost works. The resolution of localhost also seems to be working correctly. I get the following logs
localhost resolves to: [::1 127.0.0.1]
NOTE: IPV6 gets resolved first.
Though I am not able to figure what failed here. I will have end up not using localhost for now. Though, curious what is happening here.