Open Stack

Was great to see many stackers at the summit!

Following-up on one of the design discussions, the consensus seemed to be
that the operation which puts a host in maintenance mode should probably
only disable further provisioning requests to that host, while the
orchestration of migrating the individual instances from that host should
be done separately, potentially even outside of Nova. One possible approach
could be to use the admin API to list all the instances on a particular
host, and then to migrate each of them (potentially using the option not to
specify the target host, in which case the new placement will be selected
by the scheduler). Similar approach may apply to recovery of instances from
a failed host, using 'evacuate' API.

It would be great to understand how people might want to have this
capability surfaced and consumed by the administrator. A script (somehow
shared with the community)? REST API? (provided by which component?) part
of nova-manage? something else?

Would appreciate your feedback (especially if you manage OpenStack clouds
and is interested in this capability).

Thanks,
Alex

P.S. one additional item on our todo list is to enable usage of scheduler
hints when applying the individual migration operations
P.P.S. similar scenarios might be also implemented for Cinder storage
nodes, ones the new volume migration feature gets implemented