Notification System

Openstack desperately needs a system to notify interested parties of events relevant to them. More specifically, the ability to notify external consumers of events like instance builds, deletions and migrations are useful for monitoring and billing applications. We feel that a unified and defined notification system will discourage the inevitable requests for one-off implementations, and also will provide the opportunity to implement a clean, scalable solution.

As such, we're proposing Openstack uses PubSubHubBub, which uses basic REST and Atom/RSS feeds to notify subscribers of information they care about. It sees substantial use in large production websites, and we feel that it would be appropriate for us.