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.
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