[openstack-dev] [nova] Nova compute will delete all your instances if you change its hostname

Dan Smith dms at danplanet.com
Fri Feb 27 17:38:18 UTC 2015


> The hostname is a unique identifier, however, it isn't a /stable/ 
> unique identifier because it is determined at the whim of the 
> administrator.

Honestly, I think it's as stable as the administrator wants it to be. At
the level of automation that any reasonable deployment will be running,
I think it's the right thing to use, personally.

> We could instead use the host UUID which is both unique and stable. 
> That would avoid nova having to worry about administrator 
> reconfigurations in this respect.

Assuming you're talking about the DMI UUID, this is a problem if I have
a failing DIMM, swap the disks out of a box into an identical box (which
will have a different UUID) and reboot. If not, then it's an OS-level
UUID, which is persisted state, and which would change if I re-install
my boxes (puppet run) and expect my instances to remain because I
persist images, config, etc.

> IMHO if we can make nova more robust against admin changes like this,
> it'd be a good thing.  I agree that we don't want to maintain state
> and indeed this is not needed - every HV I know of has a concept of a
> host UUID it can report that'd do the job just fine.

The hostname is the unique identifier that is under the control of the
administrator. It's easily adjustable if need-be, it's as static as it
needs to be, and it's well-understood.

--Dan

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