Tomcat management using jmx4r

Something which is not obvious with the way jmx4r leverages JMX API and Ruby metaprogramming is that you can write simple scripts to manage a Java application without any dependency on the MBeans exposed by the application.

For simplicity, in my examples I always use MBeans exposed by the JVM but jmx4r works with any MBean even if its interface is unknown from the JVM running the management scripts.

Here is a simple example to manage Tomcat using jmx4r.

Let's assume that we have Tomcat running locally and manageable remotely on port 3000 (without authentication):

    $ export CATALINA_OPTS="-Dcom.sun.management.jmxremote \
        -Dcom.sun.management.jmxremote.port=3000 \
        -Dcom.sun.management.jmxremote.ssl=false \
        -Dcom.sun.management.jmxremote.authenticate=false"
    $ ./bin/catalina.sh/run

We want to know among all the Web Modules running in Tomcat which ones are privileged and which ones are not. The whole script to do so is:

    # tomcat_modules.rb
    require "rubygems"
    require "jmx4r"

    JMX::MBean.establish_connection :host => "localhost", :port => 3000

    web_modules = JMX::MBean.find_all_by_name "Catalina:j2eeType=WebModule,*"
    privileged, unprivileged = web_modules.partition { |m| m.privileged }
     
    puts "Privileged:\n"     + privileged.map   {|m| m.path }.join("\n  ")
    puts "Unprivileged:\n  " + unprivileged.map {|m| m.path }.join("\n  ")

Executing this script gives:

    $ jruby tomcat_modules.rb 
    Privileged:
      /balancer
      /manager
      /host-manager
    Unprivileged:
      /tomcat-docs
      /servlets-examples
      /jsp-examples
      
      /webdav

That's were using JRuby shines: it combines the simplicity of using directly the MBeans exposed by a Java application without having to bother with classes dependency.

Using Java to write a corresponding script means choosing your "poison":

• No class dependency but tedious (and unnatural) use of MBeanServerConnection methods to interact with Tomcat MBeans
• Use directly Tomcat MBeans (thanks to MBeanServerInvocationHandler) but you must take care having all their interfaces (and dependencies) in the class path of the JVM running the script

I can not thank enough both the JMX and JRuby guys which make it so simple to get the best of both worlds in jmx4r:

• simple to use directly the MBeans API
• simple to deploy without class dependency issues