RMI cannot connect to remote server

Question

I've been plying with RMI recently and while I managed to make it work on locahost I've been having all sorts of problem when trying to use a remote server. Here's the basic code I'm trying to run:

Server:

public class RmiServer extends UnicastRemoteObject implements RmiServerIntf {
    public static final String MESSAGE = "Hello world";

    public RmiServer() throws RemoteException {
    }

    public String getMessage() {
    return MESSAGE;
    }

    public static void main(String args[]) {
        System.out.println("RMI server started");

        if (System.getSecurityManager() == null) {
            System.setSecurityManager(new RMISecurityManager());
            System.out.println("Security manager installed.");
            } else {
                   System.out.println("Security manager already exists.");
            }

            try {
                    LocateRegistry.createRegistry(1099);
                    System.out.println("java RMI registry created.");
            } catch (RemoteException e) {
                    e.printStackTrace();
            }

            try {
                    RmiServer obj = new RmiServer();

                    Naming.rebind("rmi://localhost/RmiServer", obj);

                    System.out.println("PeerServer bound in registry");
            } catch (Exception e) {
                    e.printStackTrace();
            }
      }
}

Remote class interface:

public interface RmiServerIntf extends Remote {
    public String getMessage() throws RemoteException;
}

Client:

public class RmiClient { 
    RmiServerIntf obj = null; 

    public String getMessage() { 
        try { 
            obj = (RmiServerIntf)Naming.lookup("rmi://54.229.66.xxx/RmiServer");
            return obj.getMessage(); 
        } catch (Exception e) { 
            e.printStackTrace(); 
            return e.getMessage();
        } 
    } 

    public static void main(String args[]) {
        if (System.getSecurityManager() == null) {
            System.setSecurityManager(new RMISecurityManager());
        }

        RmiClient cli = new RmiClient();

        System.out.println(cli.getMessage());
    }
}

rmi.policy file:

grant {
permission java.security.AllPermission;
};

I compiled the classes and created a stub for the server. Then I placed client, stub, interface and policy on my machine and server, stub, interface and policy on the remote machine. The remote server being a Linux machine I made all the files executable. I also added a rule on the local firewall allowing port 1099, and opened all ports on the remote machine

After this I navigated to the server's directory on the remote machine and inserted the following command:

java -Djava.security.policy=rmi.policy RmiServer

This didn't give me problems so I went back to the local machine and entered

java -Djava.security.policy=rmi.policy RmiClient

I wait, and wait and I get the error message:

Connection refused to host: 172.31.xx.xx; nested exception is: java.net.ConnectException: Connection timed out: connect 

I've been fighting with these connection errors all day yesterday and this is as far as I got. I'm sure there's only one very small thing I'm still doing wrong but I just can't find what it is.

Answer 1

This may not solve your problem, but I've had similar issues with JPPF (via Java RMI) on Linux. The solution was to ensure that the ephemeral port range on the Client-side machine covered only ports that were allowable by the Client-side's local firewall. Eg, if your firewall allows ports 48000 to 64000 to be connected to by an external machine, ensure that your ephemeral port range also falls within 48000 to 64000. Give that a try and let us know what happens.

Answer 2

System.setProperty("java.rmi.server.hostname","10.0.3.73");

Please use the above statements in your RMIServer side code, and try and connect from remote client again. It worked for me