[Openstack-operators] [nova] Should we allow passing new user_data during rebuild?

Tomáš Vondra vondra at homeatcloud.cz
Thu Oct 5 08:22:14 UTC 2017

In our cloud, we offer the possibility to reinstall the same or another OS on a VPS (Virtual Private Server). Unfortunately, we couldn’t use the rebuild function because of the VPS‘s use of Cinder for root disk. We create a new instance and inject the same User Data so that the new instance has the same password and key as the last one. It also has the same name, and the same floating IP is attached. I believe it even has the same IPv6 through some Neutron port magic.

BTW, you wouldn’t believe how often people use the Reinstall feature.

Tomas from Homeatcloud


From: Belmiro Moreira [mailto:moreira.belmiro.email.lists at gmail.com] 
Sent: Wednesday, October 04, 2017 5:34 PM
To: Chris Friesen
Cc: openstack-operators at lists.openstack.org
Subject: Re: [Openstack-operators] [nova] Should we allow passing new user_data during rebuild?


In our cloud rebuild is the only way for a user to keep the same IP. Unfortunately, we don't offer floating IPs, yet.

Also, we use the user_data to bootstrap some actions in new instances (puppet, ...).

Considering all the use-cases for rebuild it would be great if the user_data can be updated at rebuild time.


On Wed, Oct 4, 2017 at 5:15 PM, Chris Friesen <chris.friesen at windriver.com> wrote:

On 10/03/2017 11:12 AM, Clint Byrum wrote:

My personal opinion is that rebuild is an anti-pattern for cloud, and
should be frozen and deprecated. It does nothing but complicate Nova
and present challenges for scaling.

That said, if it must stay as a feature, I don't think updating the
user_data should be a priority. At that point, you've basically created an
entirely new server, and you can already do that by creating an entirely
new server.

If you've got a whole heat stack with multiple resources, and you realize that you messed up one thing in the template and one of your servers has the wrong personality/user_data, it can be useful to be able to rebuild that one server without affecting anything else in the stack.  That's just a convenience though.


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