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.