Keep Your Tomcat Healthy

Lambda Probe is an effective tool that presents every bit of information about Tomcat Web application server in a Web-based visualized format for maintaining Tomcat's stability and availability

Saturday, March 01, 2008

Though Tomcat comes with functionality through which its administrator can monitor and manage various deployed Web applications as well as access the JMX beans and performance logs, the information gained through these logs and beans is hard to read and interpret. If a Tomcat administrator wishes to have the JVM (Java Virtual Machine) or the datasource usage information, he will get the information but in a very crude format. Now imagine if he gets the same information about JVM memory usage in a graphical format rather than just crude numbers, he would be able to interpret the information easily and it would help him take steps to avoid any memory leak.

Lambda Probe is one such Open Source tool that helps in effective monitoring and administering of the Tomcat Web application server. In this article we will explore various features of Lambda Probe through which various Tomcat runtime parameters can be monitored easily which otherwise are ignored because of the complexity to access and interpret them.

Installation
The Lambda Probe is a Java Web application archive (WAR) and is available for download as a zipped file from the site- lambdaprobe.org. Once Lambda Probe has been downloaded, you can install the extracted probe.war file onto the Tomcat Web application server either through the Tomcat's manager application or by placing the file in Tomcat's Web apps directory for deployment. The Lambda Probe application will get deployed on the Tomcat server. To access the Web application navigate to the URL-http://localhost:<PORT>/probe, where <PORT> is the port number on which the Tomcat server is configured to run (in our case, 80). Before using the Probe Web application, we will have to create new security roles for Lambda Probe.

Tomcat's roles are configured through tomcat-user.xml file. The roles to be declared are manager, poweruser, poweruserplus, and probeuser. The role of 'manager' is same as required by Tomcat Manager and provides full access to Lambda Probe functionality. While the roles of poweruser and poweruserplus are having few privileges restricted, and the role of probeuser is least privileged having just access to read-only functionalities. While making changes to tomcat-user.xml file make sure that the user tomcat is assigned the role of manager. The following code snippet defines all four roles for the Lambda probe to work on Tomcat server.

The deployed applications on Tomcat are listed; clicking on an application name will display its detailed status and options to view other attributes

<role rolename="manager"/> <role rolename="tomcat"/> <role rolename="poweruser"/> <role rolename="role1"/> <role rolename="poweruserplus"/> <role rolename="probeuser"/> <user username="both" password="tomcat" roles="tomcat,role1"/> <user username="tomcat" password="tomcat" roles="tomcat,manager, poweruser,poweruserplus,probeuser"/> <user username="role1" password="tomcat" roles="role1"/>

Now after doing the necessary changes restart the server and access the Lambda Probe application after supplying the username and password.

Features
When you navigate to the URL of the Probe application, it presents a list of all the deployed applications on the server and their status with information like number of sessions, total number of servlets requests, etc. Through the navigation tab, the user can access other features like datasource monitoring, deployment of Web apps, system information, etc. Among these features datasource monitoring, JVM memory inspection, and session inspection would be helpful to an administrator in charge of monitoring and maintaining the Tomcat server. For every Tomcat administrator the datasource pool utilization and its optimal performance is a major concern. In a production scenario a deployed application can crash if its allocated database connection pool gets exhausted. Lambda Probe comes handy here for Tomcat admins with its intuitive datasource monitoring feature, which represents each application's utilization of pooled database connection in a graphical format. Another feature is of 'Group by JDBC URL,' which helps in seeing how many total connections are being utilized actually by any given deployed application.

Memory Utilization shows the JVM's various processes on a real-time basis and in a graphical format

This particular information can help administrator to predict how many client connections are allowed by the database. The Memory Utilization feature can be found under System Information tab. This system information tab displays the summarized information of memory, OS, and container information along with option to force garbage collection if the memory utilization has increased to higher side. Sometimes end users are shown blank screens or 'Page Not Found' errors, which occur because of OutOfMemory exception errors. The JVM has an elaborate memory management that manages the working memory allocated to Java processes. Lambda Probe gives the administrator this JVM management like facility through Memory Utilization option. This helps the administrator to process and predict situations where the memory leaks may occur and hence prevent an application crash. This functionality represents the real-time JVM memory space data (PermGen, CodeCache, etc) in a graphical format. As this information is accessed through JMX (Java Management Extensions), you will have to enable the JMX to get this information displayed through Lambda Probe. This can be done by adding the JAVA_OPTS variable to the catalina.bat file. The following code line enables the JMX for Tomcat.

set JAVA_OPTS=%JAVA_OPTS%-Dcom.-sun.management.jmxremote

Besides monitoring real-time Tomcat parameters, Lambda Probe application also provides options to view the logs on real-time basis, to see what and where the problem has occurred. Also the app deployer facility is handy to directly deploy the Web archive applications through the Probe.

Conclusion
Through Lambda Probe, a Tomcat administrator can effectively monitor the production server environment where the situations like memory shortage for Tomcat apps, or sessions expiring before user's request, etc. can be averted beforehand.

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