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Monitoring Tomcat

Monitoring of a running Tomcat instance can be done in several ways, but observing a Tomcat instance via JMX beans will give you the best information available through standard interfaces (i.e. JMX). You can find information about connecting to Tomcat via JMX in the Tomcat Users' Guide. Rather than repeating that information here (which is mostly about configuration, connection, etc.), please go read the official documentation.

This page is intended to be a community-curated collection of useful JMX beans that may be useful to you after you have made your JMX connection and want to observe interesting data through Tomcat's (and other) JMX beans.

JVM Information

Heap and other Memory Information

You will certainly want to inspect your JVM's memory usage. Here are some JMX beans and attributes that can be used to do so.

  • JMX Bean: java.lang:type=Memory
  • Attribute: HeapMemoryUsage

The attribute value is a javax.management.openmbean.CompositeData which contains 4 keys: committed, init, max, and used. The 'used' key is probably the most useful (or a combination of 'used' / 'max' to get a memory-usage metric as a ratio).

  • JMX Bean: java.lang:type=MemoryPool,name=CMS Perm Gen
  • Attribute: Usage

Similar to the HeapMemoryUsage MXBean described above, this one will give you information about the "PermGen" heap generation. Depending upon your garbage collection and other memory settings, you might have different MXBeans under java.lang:type=MemoryPool with different names. You should inspect each one to determine if they would be useful for you to inspect.

Tomcat Information

Version Warning

These JMX bean names are accurate for the current version of Tomcat 7 (7.0.28 at the time of this writing). If you are using a different version of Tomcat, you may have to adjust the names of the beans identified on this page.

Thread Usage

  • JMX Bean: Catalina:type=Executor,name=[executor name]

  • Attributes: poolSize, activeCount

This is the number of threads currently in the executor's thread pool. Obviously, this is only useful if you are using an <Executor> (which you are using, of course, right?).

Request Throughput

  • JMX Bean: Catalina:type=GlobalRequestProcessor,name="[depends]"

  • Attributes: bytesSent, bytesReceived, errorCount, maxTime, requestCount
  • Operations: resetCounters

Sessions

  • JMX Bean: Catalina:type=Manager,context=[context name],host=[hostname]

  • Attributes: activeSessions

External Monitoring Tools

Plug-in-based monitoring software like Nagios and Icinga may need some help interacting with Tomcat's JMXProxyServlet. tools/check_jmxproxy.pl is a Perl script that can be used with these tools to monitor Tomcat via the JMXProxyServlet.

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