How to set up gRPC client - server correctly

Question

I have a gRPC client and a server, when I run them they seem to be running fine, but when I try to dial a server with a client I get an error:

"Error": {
    "code": 14,
    "message": "all SubConns are in TransientFailure"
},

No idea what is it. I tried to find a solution with google, no success there.

Any ideas? Here is my server code:

lis, err := net.Listen("tcp", fmt.Sprintf("%s:%d", cfg.Host, cfg.Port))
if err != nil {
    logger.Critical(ctx, "failed to listen: %v", err)
} else {
    logger.Info(ctx, "[userserver] running at %s:%d", cfg.Host, cfg.Port)
}

grpcServer := grpc.NewServer()
userServer := userserver.New()
pb.RegisterDomainServer(grpcServer, userServer)
rpcErr := grpcServer.Serve(lis)

if rpcErr != nil {
    logger.Critical(ctx, "failed to serve: %v", rpcErr)
}

btw the server here shows log:

2018/02/08 07:03:37.603287 INFO: [userserver] running at localhost:3001

and client:

conn, err := grpc.Dial(c.serverAddr, grpc.WithInsecure())
if err != nil {
    return err
}
defer conn.Close()

client := pb.NewDomainClient(conn)
_, err = client.Dispatch(ctx, &pb.Command{
    Name:    command,
    Payload: payload,
})

and this is port buff

service Domain {
  rpc Dispatch(Command) returns (Response);
}

message Command {
  string name = 1;
  bytes payload = 2;
}

message Response {}

Answer 1

Is the server listening to that port?

// Most linux 
lsof -i :3001

// OSX
lsof -iTCP -sTCP:LISTEN -P

Are you connecting the client to the right address?

c.serverAddr should be "127.0.0.1:3001"