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+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



[1] IBM and Cisco: Together for a World Class Data Center, Page 141.
http://books.google.fr/books?id=DHjJAgAAQBAJ
<http://books.google.fr/books?id=DHjJAgAAQBAJ&pg=PA141#v=onepage&q&f=false
> &pg=PA141#v=onepage&q&f=false







De : Sylvain Bauza [mailto:sylvain.bauza at gmail.com]
Envoyé : jeudi 3 avril 2014 15:52
À : OpenStack Development Mailing List (not for usage questions)
Objet : [openstack-dev] [Nova] Hosts within two Availability Zones :
possible or not ?



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].





Your comments are welcome.

Thanks,

-Sylvain





[1] : https://bugs.launchpad.net/nova/+bug/1277230



[2] :
https://github.com/openstack/nova/blob/9d45e9cef624a4a972c24c47c7abd57a72d
74432/nova/compute/api.py#L3378

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