Configure JMX over SSH instead of SSL

JmxOverSshConfigurator

/*
 * Copyright (C) 2015 Frode Carlsen.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package fc.jmx;
 
import java.io.IOException;
import java.io.Serializable;
import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.rmi.registry.LocateRegistry;
import java.rmi.server.RMISocketFactory;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
 
import javax.management.MBeanServer;
import javax.management.MalformedObjectNameException;
import javax.management.ObjectName;
import javax.management.remote.JMXConnectorServer;
import javax.management.remote.JMXConnectorServerFactory;
import javax.management.remote.JMXServiceURL;
import javax.management.remote.rmi.RMIConnectorServer;
 
import java.util.logging.Logger;
import java.util.logging.Level;
 
/** 
 * JMX configurator which allows remote connections to a Java VM over an SSH connection with an application specified port, instead of requiring SSL and having to set up certificates.
 * To use - set up port-forwarding over SSH, and connect to that port from the client.  This is achieved by only allowing connections over the loopback interface.
 * Both the RMI registry and the JMX connection are set the same, so as to avoid dynamic ports (which makes it easier to use through firewalls, iptables rules and SELinux)
 * <p>
 * Initialize on startup of application. Should only be initiailzied once as it forces certain rmi/jmx relevant properties
 * It creates a local socket proxy for jmx which can be connected to over the loopback interface.  
 * <p>
 * Beware that password authentication and roles are not enabled in the default configuration below., but are trivial to add in for the industrious reader.
*/
public class JmxOverSshConfigurator {
    private static final Logger log = Logger.getLogger(JmxOverSshConfigurator.class.getName());
    
    private final Map<String, Object> env = new HashMap<>();
 
    private final int port;
 
    private JMXConnectorServer cs;
 
    private String domain;
 
    public static synchronized JmxOverSshConfigurator initJmx(String domain, int port) {
        return startJmxAgent(domain, port);
    }
 
    private JmxOverSshConfigurator(String domain, int port) throws IOException {
        this.domain = domain;
        this.port = port;
 
        System.setProperty("java.rmi.server.randomIDs", "true");
 
        // Make sure our RMI server knows which host we're binding to
        System.setProperty("java.rmi.server.hostname", InetAddress.getLoopbackAddress().getHostAddress());
 
        LoopbackSocketFactory ssf = new LoopbackSocketFactory();
 
        env.put("com.sun.management.jmxremote.authenticate", "false");
        env.put("com.sun.management.jmxremote.ssl", "false");
 
        env.put(RMIConnectorServer.RMI_SERVER_SOCKET_FACTORY_ATTRIBUTE, ssf);
 
        LocateRegistry.createRegistry(port, null, ssf);
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
 
        // Se http://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html#gdfvq
        // Monitoring applications through a firewall
        String serviceUrl = "service:jmx:rmi://localhost:" +
                (port) + // RMIService, RMIConnection port
                "/jndi/rmi://localhost:" +
                (port) // RMIRegistry
                + "/jmxrmi";
 
        log.log(Level.CONFIG, "JMX: Trying to connect to registry : " + serviceUrl);
 
        JMXServiceURL url = new JMXServiceURL(serviceUrl);
        cs = JMXConnectorServerFactory.newJMXConnectorServer(url, env, mbs);
 
    }
 
    private void start() throws IOException {
        cs.start();
        log.log(Level.CONFIG, "JMX remote interface started at port [" + port + "]");
    }
 
    public synchronized void stop() {
        try {
            cs.stop();
        } catch (IOException e) {
            log.log(Level.INFO, "Caught IO exception while closing JMX interface", e);
        }
        log.log(Level.CONFIG, "JMX remote interface stopped for port [" + port + "]");
        stopJmx();
    }
 
    private void stopJmx() {
        removeAllMBeans(domain + ":*");
    }
 
    private static JmxOverSshConfigurator startJmxAgent(String domain, int jmxPort) {
        JmxOverSshConfigurator jmxConfigurator;
        try {
            jmxConfigurator = new JmxOverSshConfigurator(domain, jmxPort);
            jmxConfigurator.start();
            return jmxConfigurator;
        } catch (IOException e) {
            // do not throw exception, but log error, as it may fail when running over vpn
            log.log(Level.SEVERE, "Could not start JMX on port " + jmxPort, e);
            return null;
        }
    }
 
    public static void removeAllMBeans(String mbeanQuery) {
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
        Set<ObjectName> names = mbs.queryNames(createMBeanObjectNameFullyQualified(mbeanQuery), null);
        for (ObjectName objName : names) {
            try {
                mbs.unregisterMBean(objName);
            } catch (Exception ignored) { // NOSONAR
            }
        }
    }
 
    private static ObjectName createMBeanObjectNameFullyQualified(String navn) {
        try {
            return new ObjectName(navn);
        } catch (MalformedObjectNameException e) {
            throw new IllegalArgumentException("Invalid mbean name [" + navn + "]", e);
        }
    }
 
    public static class LoopbackSocketFactory extends RMISocketFactory implements Serializable {
        @Override
        public ServerSocket createServerSocket(int port) throws IOException {
            return new ServerSocket(port, 0, InetAddress.getLoopbackAddress());
        }
 
        @Override
        public Socket createSocket(String host, int port) throws IOException {
            InetAddress loopback = InetAddress.getLoopbackAddress();
            if (host.equals(loopback.getHostAddress()) || host.equals(loopback.getHostName())) {
                // just call the default client socket factory
                return RMISocketFactory.getDefaultSocketFactory()
                        .createSocket(host, port);
            } else {
                throw new UnsupportedOperationException("Only RMI connections to loopback interface supported, cannot connect to host=" + host + ", port="
                        + port);
            }
        }
    }
 
}