Using Openstack scheduler hints with juju

[Gustavo Niemeyer]

On Fri, Feb 1, 2013 at 12:23 PM, William Reade
<william.reade at canonical.com> wrote:
> On Fri, 2013-02-01 at 00:37 +0000, Martin Packman wrote:
>> A list of string uuids can also be given rather than a single string
>> uuid. Spaces are accepted by the json parser, but are a little tricky
>> to handle in constraint specification so are carefully omitted in
>> these examples.
>
> Requiring that the user worry about actual instance ids is bad juju ;).
> Would you describe the use cases that originally prompted this work? If
> they're similar to the following:
>
>   * Units of service X should be deployed to instances running on
>     different physical machines ("I want my mongos to be separated").
>   * Units of service X should be deployed to instances that are
>     running on the same physical machine as some unit of service Y
>     ("I want rabbitmq near mysql").
>
> ...then it might be that it can be usefully expressed as an assignment
> policy. The assignment policy has hitherto been underused, but is
> becoming directly relevant in the context of colocation; the short
> version is that an assignment policy is analogous to a constraint, but
> (1) is applied at a unit resolution and (2) can take state into account
> when determining what to do. Does this sound helpful to you?

Agree pretty much entirely. The only detail I'd add is that this *is*
a constraint, rather than being just analogous to one, right?
Assignment policies are an implementation detail which were not
supposed to leak up to a UI level.


gustavo @ http://niemeyer.net