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Part IV

Agent Services

The minimal and base agents presented in Part II, Agent Applications are manageable but are created empty. In this part we will examine agent services, MBeans that interact with your resources to provide management intelligence at the agent level. These services allow your agents to perform local operations on their resources that used to be performed by the remote manager. This frees you from having to implement them in the management application, and it reduces the amount of communication throughout your management solution.

In the Java dynamic management architecture, agents perform their own monitoring, avoiding constant manager polling. Agents also handle their own logical relations between objects, providing advanced operations that no longer require a relational database in the manager.

Java dynamic management agents are also much smarter, using discovery to be aware of their peers. They also connect to other agents to mirror remote resources, thus providing a single point of entry into a whole hierarchy of agents. Finally, agents are freed from their initial environment settings through dynamic downloading, allowing managers to push new classes to an agent effectively. As new resources and new services are developed, they can be loaded into deployed agents, boosting their capabilities without affecting their availability.

The benefit of agent services is increased by their dynamic nature. Agent services can come and go as they are required, either as determined by the needs of an agent's smart resources or on demand from the management application. The agent capability of self-management through the services is completely scalable: small devices might only allow monitors with some logic, whereas a server might embed the algorithms and networking capabilities to oversee its terminals autonomously.

This part contains the following chapters:

  • Chapter 12, M-Let Class Loader shows how the m-let class loader downloads new classes to the agent from a given URL (Universal Resource Locator). An m-let is a management applet: the HTML-style tag at the target URL that contains information about the classes to download. A manager can store new MBean classes anywhere, update its m-let file to reference them, and instruct an agent to load the classes. The new classes are created as MBeans, registered in the MBean server and ready to be managed.

  • Chapter 13, Relation Service shows how the relation service creates associations between MBeans, allowing for consistency checking against defined roles and relation types. New types can be defined dynamically to create new relations between existing objects. All relations are managed through the service so that it can expose query operations for finding related MBeans. Relations themselves can also be implemented as MBeans, allowing them to expose attributes and operations that act upon the MBeans in the relation.

  • Chapter 14, Cascading Service shows how cascading agents allow a manager to access a hierarchy of agents through a single point-of-access. The subagents can be spread across the network, but their resources can be controlled by the manager through a connection to a single master agent. MBeans of a subagent are mirrored in the master agent and respond as expected to all management operations, including their removal. No special proxy classes are needed for the mirror MBean, meaning that every MBean object can be mirrored anywhere without requiring any class loading.

  • Chapter 15, Discovery Service describes how the discovery service lets applications find Java dynamic management agents that are configured to be found. Using active discovery, the client broadcasts a discovery request over the network. Agents that have a discovery responder registered in their MBean server will automatically send a response. The client can then keep a list of reachable agents by using passive discovery to detect when responders are activated and deactivated. Along with the agent's address, the discovery response contains version information from the agent's delegate MBean and the list of available protocol adaptors and connectors.

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