If a node has been out of contact with the Controller for a certain amount of time, the Controller marks the node as a historical node. The Controller suspends certain types of processing activities for the node (such as rule evaluation), but continues to present data for the node in the UI.
If the node resumes contact with the Controller before the node deletion period expires, the Controller restores it to an active state. Otherwise, it is permanently removed from the Controller and the node level data is no longer accessible in the UI. However, the tier- and application-level historical metric data for the node remain available even after the node is deleted.
By default, the Controller considers a node historical after about 20 days of inactivity and deletes the node after 30 days. For a highly dynamic application environment in which nodes are created and destroyed frequently, it usually makes sense to shorten the node activity timeout period. This allows recycled nodes to be treated as such in the Controller.
Another consideration for historical nodes is that their names can be assigned to new nodes if node name reuse is enabled. Node name reuse is an App Agent for Java option that allows the Controller to present data generated by multiple, short-lived nodes in a given tier as a single logical node.
For licensing purposes, the Controller releases the license for the agent if the Controller has not received data from the agent in the previous 5 minutes. This license availability behavior is not affected by the historical node status or node deletion timeout settings.
The node activity settings are global settings that the root AppDynamics administrator can modify from the administration console, as follows.