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some time ago Aljona showed
how to monitor and manage your java application with jmx

I'm going to show, how you can make use of JMX from the viewpoint of a sysadmin.

initial point:

You have a Java-application deployed in an applicationserver like JBoss or Tomcat and you want to monitor the health of this application(including the applicationserver and the Java-virtual-machine it is running in) with a tool like Nagios.

Use Jolokia on the server-side!

jolokia
Why do i have to use an extra Agent for this? My applicationserver is able to use Mbeans.

Of course you don't have to, but Jolokia is a HTTP/JSON bridge, which means jolokia can be accessed via HTTP and responds with JSON, that is cool, isn't it?
There are some more advantages like bulk-requests and it supports cubism.js since version 1.0.5 (Jonathan uses this to get some nicely visualized charts) … and it's fast.
Just deploy it into your applicationserver it isn't that big.

As a sysadmin i don't want to code Java nor do i want to have a JVM running on my Nagios-server, i'm used to use perl (just to satisfy any prejudices), so i stumbled over jmx4perl and decided to make use of this.

I installed jmx4perl and read the documentation.

cpan[1]> install JMX::Jmx4Perl

The tools brought along by jmx4perl are really very useful:

  1. The commandlinetool j4psh is awesome, you can browse the JMX Mbeans in color by using "cd" and "ls" with "cat" you can get the value of an attribute… tab-completion as a matter of course.
  2. With the commandlinetool jmx4perl you can easily test requests and get responses in various forms.

Time to hack:

First Nagios-test we assemble is for monitoring heapspace of the JVM, not only because it's often referenced in the documentation but rather because thats often a useful information to identify memory leaks and to know when it's time to restart the application(server). But you can follow most of the following steps for many other use cases too.

  1. be sure you got the relevant permissions in jolokia (jolokia-access.xml)
  2. search for older Nagios-Plugins and c'n'p the generic parts…
  3. search for the Mbean with j4psh or use type search of jolokia and look for interesting attributes/operations
  4. j4psh_screenshot

  5. test the request you have in your mind with e.g jmx4perl
  6. canonicalize the request
  7. my $request = new JMX::Jmx4Perl::Request({
                                              type => READ,
                                              mbean => "java.lang:type=Memory",
                                              attribute => "HeapMemoryUsage",
                                             });
    #print(Dumper($request));
    my $response = $jmx->request($request);
    #print(Dumper($response));
  8. dereference the response as you need
  9. my $used_memory=$response->value()->{'used'};
    my $max_memory=$response->value()->{'max'};
  10. start a heated debate about sensible values for warning and critical
  11. deploy your Nagios-plugin
    1. copy the script into your plugin-folder of your Nagios-server
    2. install all missing libraries on the Nagios-server
    3. define the command in commands.cfg
    4. define command{
        command_name check_jmx4perl_heapspace.pl
        command_line $USER1$/check_jmx4perl_heapspace.pl $HOSTADDRESS$ $ARG1$
      }
    5. make use of the new command in your services.cfg (or whatever you've called your file)
    define service{
      use                 remote-service
      host_name           jolokia-host
      service_description HeapSpace of JavaApp
      check_command       check_jmx4perl_heapspace.pl!8084
    }
    
  12. lean back while watching the heapspace grow…

get the complete Nagios-plugin from github



2 Responses to How Sysadmins monitor your Java application with JMX

  1. Roland Huss says:

    Thanks for the blog and using jmx4perl/jolokia ;-). However, I wonder why you are not using check_jmx4perl which comes packaged with jmx4perl. It supports tons of configuration options, various kind of checks (absolute, relative, incremental), has a 30-page documentation and, probably best, has already about 20 to 30 checks for various applications servers out of the box. Maybe you can give it a try …



  2. So i decided to code it myself because
    * its easy ;)
    * and it seems to be more flexible if you want to realize more complex things like an jmx-eventhandler to automatically flush ManagedConnectionspools with the same technic (i want to blog about that too) but yeah i should have mentioned this.
    In my next blog i will show the advantages of check_jmx4perl (it’s not always clever to reinvent the weel)
    Thx for reading!


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