Cloned from launchpad blueprint https://blueprints.launchpad.net/heat/+spec/scale-down-plug-point.
The member termination policy for heat scaling groups is currently fixed. Members are removed from the beginning of the list, effectively oldest first. The proposal is to augment the termination policy in two ways; policies contributed by the operator through a plug point would first filter the member list, and then a user-modifiable set of built-in policies would further filter the member list, resulting in a selection of a group member to remove.
Specification URL (additional information):