Open Stack

On 9/16/13 10:37 PM, Dolph Mathews wrote:
>
> On Mon, Sep 16, 2013 at 5:31 AM, Michael Still <mikal at stillhq.com 
> <mailto:mikal at stillhq.com>> wrote:
>
>     On Fri, Sep 13, 2013 at 7:51 AM, Dolph Mathews
>     <dolph.mathews at gmail.com <mailto:dolph.mathews at gmail.com>> wrote:
>
>     > ++ Data backups are a solved problem, and no DB admin should
>     trust an
>     > application to perform its own backups.
>
>     I'm not completely sure I agree. Consider the case where a cloud with
>     active users undertakes an upgrade. The migrations run, and they allow
>     user traffic to hit the installation. They then discover there is a
>     serious problem and now need to rollback. However, they can't just
>     restore a database backup, because the database is no longer in a
>     consistent state compared with the hypervisors -- users might have
>     created or deleted instances for example.
>
>
>     In this scenario if we could downgrade reliably, they could force a
>     downgrade with db sync, and then revert the packages they had
>     installed to the previous version.
>
>     How would they handle this scenario with just database backups?
>
>
> Great point, but I still wouldn't *rely* on an application to manage 
> it's own data backups :)

I don't think Michael was saying anybody should be relying on migrations 
to manage its own backups but that it could serve an edge case that 
database snapshots can not. In the scenario given I would imagine that 
the administrators did have backups but wanted to avoid using them to 
not lose any new data entered. If the migration downgrade were to fail 
they would still have the backups and be no worse off than they would 
have been without them. However if the migration downgrade works then 
they get the benefit of not (necessarily) losing new user data.

Cheers,
Josh

--
Rackspace Australia

>
>     Michael
>
>     --
>     Rackspace Australia
>
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> -- 
>
> -Dolph
>
>
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