On 04/03/2014 07:51 AM, Sylvain Bauza wrote:

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.


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