Open Stack

On 09/15/2015 02:25 AM, Daniel P. Berrange wrote:

> Taking a host offline for maintenance, should be considered
> equivalent to throwing away the existing host and deploying a new
> host. There should be zero state carry-over from OpenStack POV,
> since both the software and hardware changes can potentially
> invalidate previous informationm used by the schedular for deploying
> on that host.  The idea of recovering a previously running guest
> should be explicitly unsupported.

This isn't the way the nova code is currently written though.

By default, any instances that were running on that compute node are going to 
still be in the DB as running on that compute node but in the "stopped" state. 
If you then do a "nova start", they'll try to start up on that node again.

Heck, if you enable "resume_guests_state_on_host_boot" then nova will restart 
them automatically for you on startup.

To robustly do what you're talking about would require someone (nova, the 
operator, etc.) to migrate all instances off of a compute node before taking it 
down (which is currently impossible for suspended instances), and then force a 
"nova evacuate" (or maybe "nova delete") for every instance that was on a 
compute node that went down.

Chris