A custom action is typically used to integrate third party alerting and ticketing systems. A custom action is different from other actions in that it executes just once on the controller instance.
The custom action is made up of a custom action script and a custom.xml file, which you must create before you can create an action that uses them. The custom action scripts include parameters for specifying the affected entity, for example the tier, node, business transaction, etc. See Build a Custom Action for details on how to create the custom action script and xml file.
Custom actions are commonly used when you want to trigger a human work flow or leverage an existing alerting system that is external to AppDynamics. For example, you could use a custom action to file a JIRA ticket when AppDynamics reports that a connection pool is near saturation.
After the custom action script and custom.xml files have been tested manually and installed on the Controller and you have restarted the Controller, you can create the custom action.
The custom action is now available for assignment to a policy.