Comment 1 for bug 1269534

The problem is that Heat is not aware of any out-of-band events. Periodically polling nova to retrieve instance status is not a good idea. So I have tried to detect this kind of events using ceilometer. Actually, instance lifecycle events are reported upwards from the hypervisor to nova, and nova is generating notifications that can be received by ceilometer. The only missing link is to have ceilometer to notify Heat about these events, e.g. compute.instance.delete.end.

There are two barriers to get this done:
1. Ceilometer support to alarms based on events (rather than meters). There has been work on this, but abandoned. I'm trying to resurrect that work.
2. This kind of alarms are not expected by Heat, thus Heat won't subscribe to them. When this event does happen, we need a proper authentication to invoke resource_signal, because we don't have alarm_url, and we don't have domain user credentials.