Novell® Identity Manager includes two utility drivers, Null Service and Loopback Service, whose purpose is to implement custom behavior through policies established on the drivers’ Subscriber and Publisher channels. Like other service drivers such as Entitlement and Workflow, the Null Service and Loopback Service drivers do not connect to external applications or systems.
The Null Service driver performs any tasks that are implemented through policies on the Subscriber channel. The Publisher channel is not used; the driver does not connect the Subscriber channel to the Publisher channel, but rather acts as a sink for most operations, simulates doing something with operations, and then returning success. Typical uses for the Null Service driver include the following:
Adding the classes and attributes that you want to monitor for change in the Subscriber Filter as for the class and for the attribute.
Adding Subscriber Event Transformation policies that react to specific object or attribute changes, and performing actions such as:
Making modifications back into the Identity Vault (using actions that manipulate source attributes and objects).
Sending e-mail.
Generating custom Audit Events.
Calling extension functions to communicate the change outside of Identity Manager.
Adding a final Subscriber Event Transformation policy that vetoes all events.
The Null Service driver should be sufficient for the majority of the tasks you’ll want to perform. However, if you need to process policies on both the Subscriber and Publisher channels, you can use the Loopback Service driver instead. The only difference between the two drivers is that the Loopback driver’s Subscriber channel connects to the Publisher channel so that events can also be processed on the Publisher channel.