Keep Your Tomcat Healthy

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:/probe, where 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

roles="tomcat,role1"/> 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.