trigger notifications when lock or unlock instances for OpenStack Compute (nova)

Watcher is a project for optimization, by migrating instances among hosts. It builds a compute model at the begenning, and update it by notifications. When one instance is locked by end users, it is excepted to send a regular notification from Nova, so Watcher will update its compute model and not migrate the locked...

cluster maintenance for watcher

Sometimes we need to maintain compute nodes, update hardware and software, and so on. But we don't want user's application to be interrupted. This issue imports one goal and strategy for manually maintaining without user's application interruption.