Explain JMX URL

Question

I am trying to understand a JMX service URL.

service:jmx:rmi://192.168.30.10:1234/jndi/rmi://192.168.30.10:2344/jmxrmi

It would be great, if someone can help me understand this.

Thanks

Answer 1

I will reuse an answer I wrote up earlier for this question: Cannot connect to Tomcat's MBeanServer via jconsole in Java6

It's not complete, but might help:

Suppose you have the JMX Server (alias 'JMX Agent' alias 'the JVM you want to connect to') running on 'TARGET MACHINE' with the RMI registry port at 'RMI REGISTRY PORT' and the JMX RMI server port at 'JMX RMI SERVER PORT'.

Note:

1. The RMI registry tells JMX clients where to find the JMX RMI server port; information can be obtained under key jmxrmi.
2. The RMI registry port is generally known as it is set through system properties at JVM startup.
3. The JMX RMI server port is generally not known as the JVM chooses it at random (if no other precautions are taken).

The following URI will lead to successful connection (tested)

service:jmx:rmi://<TARGET_MACHINE>:<JMX_RMI_SERVER_PORT>/jndi/rmi://<TARGET_MACHINE>:<RMI_REGISTRY_PORT>/jmxrmi

This looks nasty. Let's cut it apart.

This URI is an RFC2609 "Service Location Protocol URL" (well, it's really an URI, right?)

It is composed of:

• service - a constant
• jmx:rmi - the service type composed of: abstract type jmx and URL scheme rmi
• the rest - the sap (service access protocol specification)

sap is decomposed into:

• //<TARGET_MACHINE>:<JMX_RMI_SERVER_PORT> - ipsite
• /jndi/rmi://<TARGET_MACHINE>:<RMI_REGISTRY_PORT>/jmxrmi - URL part

A well-informed JMX client connects to the "ipsite" to do JMX-over-RMI exchanges; but what of the JMX client that doesn't KNOW that port? Patience...

URL part is decomposed into:

• /jndi/ - This seems to tell the JMX client that it can get lookup information at the location that follows
• rmi://<TARGET_MACHINE>:<RMI_REGISTRY_PORT>/jmxrmi - Yep, we get information about the JMX RMI Server at the RMI registry, under the lookup key jmxrmi

This is somewhat cart-before-horse, as one has to contact the RMI registry given by the latter part of the SLP URL first.

After scratching head, intuitively, let's try:

service:jmx:rmi://<TARGET_MACHINE>/jndi/rmi://<TARGET_MACHINE>:<RMI_REGISTRY_PORT>/jmxrmi

Yes, that works! The JMX RMI server port is nicely obtained from the registry. On second thoughts, the target machine should also be obtained from the registry, thus:

service:jmx:rmi:///jndi/rmi://<TARGET_MACHINE>:<RMI_REGISTRY_PORT>/jmxrmi

Even better, that works, too!

References:

1. http://download.oracle.com/javase/6/docs/api/javax/management/remote/rmi/package-summary.html
2. http://download.oracle.com/javase/6/docs/api/javax/management/remote/JMXServiceURL.html
3. http://mx4j.sourceforge.net/docs/ch03s04.html
4. http://download.oracle.com/javase/6/docs/technotes/guides/management/agent.html#gdevg
5. http://www.rfc-editor.org/rfc/rfc2609.txt