WebLogic Server 12.2.1 added support for the elastic scaling of dynamic clusters:
Elasticity allows you to configure elastic scaling for a dynamic cluster based on either of the following:
Manually adding or removing a running dynamic server instance from an
active dynamic cluster. This is called on-demand scaling. You can
perform on-demand scaling using the Fusion Middleware component of
Enterprise Manager, the WebLogic Server Administration Console, or the
WebLogic Scripting Tool (WLST).
Establishing policies that set the conditions under which a dynamic
cluster should be scaled up or down and actions that define the scaling
operations themselves. When the conditions defined in the scaling policy
occur, the corresponding scaling action is triggered automatically.
To see this in action, a set of video demonstrations have been added to the youtube.com/OracleWebLogic channel that show the use of various elastic scaling options available.