A WebLogic domain can be configured to support SNMP by enabling the SNMP agent, which runs on the Administration Server. This SNMP agent can be configured to respond to requests about managed resources and deployments within the WebLogic domain. It also can be configured to fire events called trap notifications when certain attributes on resources exceed specified threshold values. Much of this sounds very similar to the JMX infrastructure described in Chapter 20, and indeed you will find that the resources that can be managed through the SNMP agent mirror the JMX managed resources. WebLogic's SNMP trap notification mechanism is built around the standard JMX monitoring and notification system. This allows you to configure the SNMP agent to send trap notifications on changes in attribute values, on configured monitor policies, and on log messages. Traps also can be sent when the Administration Server boots, or when any Managed Server comes up or goes down.
In general, a system administrator would configure WebLogic's SNMP agent to monitor information of interest, and then employ some external management system to pull information from WebLogic's SNMP agent and react to the trap notifications sent to it. WebLogic's SNMP agent would typically be part of larger network management framework that is being monitored alongside other distributed SNMP agents. WebLogic's SNMP agent also can serve as a proxy, routing requests for certain resources through to some other SNMP agent. This entire infrastructure is depicted in Figure 22-1.
Figure 22-1. WebLogic's SNMP infrastructure
Note that you can configure only a single SNMP agent for a WebLogic domain, and it must run on the Administration Server. When the SNMP agent receives a request for any information on one of its Managed Servers, the agent on the Administration Server fetches the information from the Managed Server. WebLogic's SNMP agent also contains a configurable cache, which it uses to cache the information obtained from Managed Servers in response to queries.
Managing the Web Server
Using JNDI and RMI
Using CMP and EJB QL
Packaging and Deployment
Performance, Monitoring, and Tuning
Logging and Internationalization