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We can make bidirectional dependencies, just like our deployment tasks do.

And, btw, standalone-* roles may have a restriction that at least one
node is required. I think it's ok for the plugin is case, since if you
don't want to use it - just disable it.

On Wed, Oct 21, 2015 at 1:15 PM, Dmitriy Shulyak <dshulyak at mirantis.com> wrote:
> But it will lead to situations, when certain plugins, like
> standalone_rabbitmq/standalone_mysql will need to overwrite settings on
> *all*
> dependent roles, and it might be a problem.. Because, how plugin developer
> will be able to know what are those roles?
>
> On Wed, Oct 21, 2015 at 1:01 PM, Igor Kalnitsky <ikalnitsky at mirantis.com>
> wrote:
>>
>> Hi Dmitry,
>>
>> > Insert required metadata into roles that relies on another roles, for
>> > compute it will be something like:
>> >
>> >     compute:
>> >         requires: controller > 1
>>
>> Yeah, that's actually what I was thinking about when I wrote:
>>
>> > Or should we improve it somehow so it would work for one nodes,
>> > and will be ignored for others?
>>
>> So I'm +1 for extending our meta information with such dependencies.
>>
>> Sincerely,
>> Igor
>>
>> On Wed, Oct 21, 2015 at 12:51 PM, Dmitriy Shulyak <dshulyak at mirantis.com>
>> wrote:
>> > Hi,
>> >
>> >> Can we ignore the problem above and remove this limitation? Or should
>> >> we improve it somehow so it would work for one nodes, and will be
>> >> ignored for others?
>> >
>> > I think that this validation needs to be accomplished in a different
>> > way, we
>> > don't need 1 controller for the sake of 1 controller,
>> > 1 controller is a dependency of compute/cinder/other roles. So from my
>> > pov
>> > there is atleast 2 options:
>> >
>> > 1. Use tasks dependencies, and prevent deployment in case if some tasks
>> > relies on controller.
>> > But the implementation might be complicated
>> >
>> > 2. Insert required metadata into roles that relies on another roles, for
>> > compute it will be something like:
>> >    compute:
>> >      requires: controller > 1
>> > We actually have DSL for declaring such things, we just need to specify
>> > this
>> > requirements from other side.
>> >
>> > But in 2nd case we will still need to use tricks, like one provided by
>> > Matt,
>> > for certain plugins. So maybe we should spend time and do 1st.
>> >
>> >
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