Open Stack

+1 for AZs not sharing hosts.

Because it’s the only mechanism that allows us to segment the datacenter.
Otherwise we cannot provide redundancy to client except using Region which
is dedicated infrastructure and networked separated and anti-affinity
filter which IMO is not pragmatic as it has tendency of abusive usage.
Why sacrificing this power so that users can select the types of his
desired physical hosts ? The latter can be exposed using flavor metadata,
which is a lot safer and more controllable than using AZs. If someone
insists that we really need to let users choose the types of physical
hosts, then I suggest creating a new hint, and use aggregates with it.
Don’t sacrifice AZ exclusivity!

Btw, there is a datacenter design called “dual-room” [1] which I think
best fit for AZs to make your cloud redundant even with one datacenter.

Best regards,

Toan

> -----Message d'origine-----
> De : Chris Friesen [mailto:chris.friesen at windriver.com]
> Envoyé : jeudi 3 avril 2014 16:51
> À : openstack-dev at lists.openstack.org
> Objet : Re: [openstack-dev] [Nova] Hosts within two Availability Zones :
possible
> or not ?
>
> On 04/03/2014 07:51 AM, Sylvain Bauza wrote:
> > Hi,
> >
> > I'm currently trying to reproduce [1]. This bug requires to have the
> > same host on two different aggregates, each one having an AZ.
> >
> > IIRC, Nova API prevents hosts of being part of two distinct AZs [2],
> > so IMHO this request should not be possible.
> > That said, there are two flaws where I can identify that no validation
> > is done :
> >   - when specifying an AZ in nova.conf, the host is overriding the
> > existing AZ by its own
> >   - when adding an host to an aggregate without AZ defined, and
> > afterwards update the aggregate to add an AZ
> >
> >
> > So, I need direction. Either we consider it is not possible to share 2
> > AZs for the same host and then we need to fix the two above scenarios,
> > or we say it's nice to have 2 AZs for the same host and then we both
> > remove the validation check in the API and we fix the output issue
> > reported in the original bug [1].
>
> Currently host aggregates are quite general, but the only ways for an
end-user
> to make use of them are:
>
> 1) By making the host aggregate an availability zones (where each host
is only
> supposed to be in one availability zone) and selecting it at instance
creation
> time.
>
> 2) By booting the instance using a flavor with appropriate metadata
(which can
> only be set up by admin).
>
>
> I would like to see more flexibility available to the end-user, so I
> think we should either:
>
> A) Allow hosts to be part of more than one availability zone (and allow
> selection of multiple availability zones when booting an instance), or
>
> B) Allow the instance boot scheduler hints to interact with the host
> aggregate metadata.
>
> Chris
>
>
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