Monitoring and Managing Tomcat with JMX

Starting with Java SE 5 there are features known as Monitoring and Management (M and M). The M and M platform and tools support enable applications to be monitored and managed in real-time, the technology that performs this is called Java Management Extension (JMX). JMX can monitor and managed multiple Tomcat instances remotely, Tomcat 6 is JMX-ready, it exposes a set of Java-based objects for external management. This set of objects provides runtime control for operating tuning/tweaking and runtime statistics for monitoring, they can be accessed locally or remotely using agents.

JMX Architecture

JMX is the subject matter of JSR-3, a specification developed over several years by an industry-wide network management experts group that is part of the Java Community Process (JCP). The group delivered the following specification

• A set of specifications with a detailed architectural framework, including detailed description of required components and their operations
• A functional reference implementation, with associated documentation
• A compatibility test suite to test compliance with the specification

In the world today we have a standard that already can monitor hardware devices called simple network management protocol (SNMP), but it is very restrictive to modern day software services, also SNMP is very vendor specific. JMX was designed to be flexible and adaptive from the start, by not being very vendor specific and can coexist with SNMP.

The architecture of JMX is layered as well as modular, the layers are loosely coupled. Each layer within JMX is called a level and there are three levels, each level is defined in its own specification create by different group of experts.

• Instrumentation
• Agent
• Distributed Services

Instrumentation Level

Within the instrumentation level resources and objects that can be managed and monitored are enumerated, the act of defining what can be managed and monitored is called Instrumentation. For an example a WEb application may be candidate for JMX management which entails the creation of Managed Beans (MBeans).

MBeans are Java components that live within the instrumentation level, they present a well-defined Java interface for the resource (hardware, software, application, Tomcat, etc) being managed, below is the high-level anatomy of an MBean.

Conceptually, MBeans are similar to JavaBeans and expose attributes, operations and notification events that can be caught by other levels. MBeans are oblivious to the agent that may be managing them, enabling instrumented resources to managed by any JMX-compliant system.

Agent Level

At the agent level, the MBeans exposed by the instrumentation level are aggregated by the agent logic and presented as manageable entities to higher-level distributed services and management applications. The interfaces exposed by the MBean my be presented the same or different by the agent depending on what the management system wants. The components that reside at the agent level are

• MBean Server - Aggregates MBeans, receives runtime registration of MBeans and makes them available for external management via connectors and protocol adapters
• Connectors and Adapters - provides external access to the MBeans and service aggregated by the MBean server
• Agent Services - A mandatory standard set of services that are available to a developer creating MBeans or agent logic

The MBean server is a component in the agent that aggregates the MBeans being exposed by the agent. A managed device or service needs to register the MBeans with the MBean server before it can be accessed, this happens at runtime.

The Mbean server component has no direct means of communicating with the external application, instead the MBean server relies on available connectors and protocol adapters to interface with external applications. Connectors can use many remote-access mechanisms (RMI, COBRA, Java Socket, etc).

JMX specifies a set of mandatory services that every compliant agent implementation must provide. These services including the following

• A dynamic class loading service for load management applets (mlets)
• A monitoring service to monitor changes in specified MBean attributes
• A timer service for periodic or one-shot timing
• A relation service for enforcing relationships between MBeans

Agents services allow developers to implement customized agent logic and management applications.

Distributed Services Level

This level includes applications and services that access functionality provided by the agent. At this level the management applications interact with the agent level. This is still a work in progress and thus documentation is limited.

Anthology of MBeans

MBeans are software modules that expose the capabilities of a hardware device, a software service or a software component. The following is a list of MBean types

JMX Manageable Elements

Almost all configurable elements of Tomcat will become JMX-manageable in the future, MBeans will be incorporated into all new attributes which then can be managed and monitored. Below is a small list of what MBeans are exposed in Tomcat

• Manageable Tomcat 6 architectural components - Service, Server, Engine, Connector and Host
• Manageable nested components - Realm, Logger, Value and Manager
• Manageable runtime data objects - UserDatabase, User and Role
• Manageable resource objects - NamingResource, Environment, Resource, ResourceLink, WebModule, RequestProcessor, Cache, ThreadPool

The MBeans are access by the using the following

• The JMX proxy of the Manager application(this is an HTTP protocol adapter)
• The RMI connector

Manageable Tomcat Architectural Components

Manageable Nested Components

Manageable Runtime Data Objects

Manageable Resource Objects

Exposed Application-Related Objects

Exposed Internal Tomcat Objects

Accessing JMX via the Manager Proxy

The Manager application has a JMX proxy that can be used to interact with Tomcats agent directly. The proxy enables monitoring of Tomcat components through the exposed MBeans. It also enables you to read the value of an MBean attribute, or change/set the value of a writeable MBean attributes.

There is a URL for working with the JMX proxy and you provide the operation details to the URL

Using jconsole GUI

You can also use the jconsole GUI to monitor Tomcat as well, you need to add support for this, so follow below

Once you have done this then start the jconsole (see below picture) and connect using the remote process option and using localhost:8999

then you should get the below screen, the jconsole will start collecting and displaying the Tomcat statistics, etc.