Java Management Extensions (JMX) is a framework that provides a standard way of exposing Java resources, for example, application servers,
to a system management infrastructure. Using the JMX framework, a provider can implement functions, such as listing the configuration settings, and editing the settings. This framework also includes a notification layer that management
applications can use to monitor events such as the startup of an application
server.
JMX key features
The key features of the WebSphere Application Server Version 6 implementation of JMX include:
All processes that run the JMX agent.
All run-time administration that is performed through JMX operations.
Connectors that are used to connect a JMX agent to a remote JMX-enabled management application. The following connectors are supported:
Remote Method Invocation over the Internet Inter-ORB Protocol (RMI-IIOP)
JMX Connector
Protocol adapters that provide a management view of the JMX agent through a given protocol. Management applications that connect to a protocol adapter are usually specific to a given protocol.
The ability to query and update the configuration settings of a run-time object.
The ability to load, initialize, change, and monitor application components and resources during run-time.
JMX architecture
The JMX architecture is structured into three layers:
Instrumentation layer - Dictates how resources can be wrapped within special Java beans, called managed beans (MBeans).
Agent layer - Consists of the MBean server and agents, which provide a management infrastructure. The services that are implemented include:
Monitoring
Event notification
Timers
Management layer - Defines how external management applications can interact with the underlying layers in terms of protocols, APIs, and so on. This layer uses an implementation of the distributed services specification (JSR-077),
which is not yet part of the Java 2 platform, Enterprise Edition (J2EE) specification.
The layered architecture of JMX is summarized in the following figure:
Figure 1: JMX architecture
JMX distributed administration
The following figure shows how the JMX architecture fits into the overall distributed administration topology of a Network Deployment environment:
Figure 2: WebSphere Application Server distributed administration of JMX
The key points of this distributed administration architecture include:
Internal MBeans that are local to the Java virtual machine (JVM) register with the local MBean server.
External MBeans have a local proxy to their MBean server. The proxy registers with the local MBean server. Using the MBean proxy the local MBean server can pass the message to an external MBean server that is located on:
A node agent that has an MBean proxy for all the servers within its node.
The MBean proxies for other nodes are not used.
The deployment manager has MBean proxies for all the node agents in the cell.
JMX Mbeans
WebSphere Application Server provides a number of MBeans, each of which have different functions and operations available. For example, an application
server MBean can expose operations such as start and stop. An application MBean can expose operations such as install and uninstall. Some JMX usage scenarios that you can encounter include:
External programs that are written to control the Network Deployment run time and its WebSphere resources by programmatically accessing the JMX API.
Third-party applications that include custom JMX MBeans as part of the deployed code, supporting the JMX API management of application components and resources.
The following example illustrates how to obtain an MBean:
Using Jacl:
set am [$AdminControl queryNames type=ApplicationManager,process=server1,*]
Using Jacl:
am = AdminControl.queryNames('type=ApplicationManager,process=server1,*')
Each WebSphere Application Server runtime MBean may have attributes, operations,
and notifications. The complete documentation for each MBean supplied with WebSphere Application Server is available in an html table that is installed in each copy of the WebSphere Application Server product. Under the main install directory for the product, there is a directory named web. And under that directory is another directory called mbeanDocs. In the mbeanDocs directory are several html files, one for each supplied with WebSphere Application Server.
There is also an index.html file that ties all the individual MBean files together in a top-level navigation tree. Each MBean provides summary of its attributes, operations, and notifications.
JMX benefits
The use of JMX for management functions in WebSphere Application Server provides the following benefits:
Enables the management of Java applications without significant investment.
Relies on a core-managed object server that acts as a management agent.
Java applications can embed a managed object server and make some of its functionality available as one or several MBeans that are registered with the object server.
Provides a scalable management architecture.
Every JMX agent service is an independent module that can be plugged into the management agent.
The API is extensible, allowing new WebSphere Application Server and custom application features to be easily added and exposed through this management interface.
Integrates existing management solutions.
JMX smart agents are capable of being managed through HTML browsers or by various management protocols such as Web services, Java Message Service (JMS), and Simple Network Management Protocol (SNMP).
Each process is self sufficient when it comes to the management of its resources. No central point of control exists. In principle, a JMX-enabled management client can be connected to any managed process and interact with the MBeans that are hosted by that process.
JMX provides a single, flat, domain-wide approach to system management.
Separate processes interact through MBean proxies that support a single management client to seamlessly navigate through a network of managed processes.
Defines the interfaces that are necessary for management only.
Provides a standard API for exposing application and administrative resources to management tools.
