A diagnostic system module is a configurable software component that monitors aspects of running server instances. You can configure diagnostic system modules to monitor single, stand-alone server instances, selected server instances in a cluster, or all the server instances in a cluster.
A single diagnostic module can be targeted to one or more server instances and/or clusters at a time. However, only one module can be targeted to a given server instance at one time. Diagnostic modules are not available for monitoring domains.
Once you have created the diagnostic system module, you can configure metrics, watches and notifications, and instrumentation (diagnostic monitors).