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On 01/07/14 16:30, Mike Spreitzer wrote:
> Thinking about my favorite use case for lifecycle plug points for cloud
> providers (i.e., giving something a chance to make a holistic placement
> decision), it occurs to me that one more is needed: a scale-down plug
> point.  A plugin for this point has a distinctive job: to decide which
> group member(s) to remove from a scaling group (i.e.,
> OS::Heat::AutoScalingGroup or OS::Heat::InstanceGroup or
> OS::Heat::ResourceGroup or AWS::AutoScaling::AutoScalingGroup).  The
> plugin's signature could be something like this: given a list of group
> members and a number to remove, return the list of members to remove
> (or, equivalently, return the list of members to keep).  What do you think?

I think you're not thinking big enough ;)

There exist a whole class of applications that would benefit from 
autoscaling but which are not quite stateless. (For example, a PaaS.) So 
it's not enough to have plugins that place the choice of which node to 
scale down under operator control; in fact it needs to be under 
_application_ control.

This is on the roadmap, and TripleO really needs it, so hopefully it 
will happen in Juno.

cheers,
Zane.