Affinity instance slot reservation

Bug #1630929 reported by daniel.pawlik on 2016-10-06
This bug affects 1 person
Affects Status Importance Assigned to Milestone
OpenStack Compute (nova)

Bug Description

Currently ServerGroupAffinityFilter schedules all instances of a group on the same host, but it doesn't reserve any slots for future instances on the host.


When user_1 would spawns 3 instances with affinity server group policy, all the instances will be scheduled on the same host (host_A).
If user_2 also spawns instances and they are placed on host_A, quota of max_instances_per_host will be reached, so user_1 can not add 2 new instances to the same server group and error "No valid host found" will be returned.

My proposition is to add new parameters to nova.conf to configure ServerGroupAffinityFilter:
- enable_slots_reservation (Boolean)
- reserved_slots_per_instance (-1 will count difference between max_instances_per_host and quota_server_group_members ; values bigger than 0 will reserve the indicated number of ports per group)

Nova scheduler checks if on a host there are any instances with affinity policy and based on that, it counts available slots.

Sylvain Bauza (sylvain-bauza) wrote :

Nova doesn't have (yet) in its scope to manage instance allocations and that really looks like a new feature that should be discussed in a spec.

Changed in nova:
status: New → Opinion
importance: Undecided → Wishlist

Fix proposed to branch: master

Changed in nova:
assignee: nobody → daniel.pawlik (daniel-pawlik)
status: Opinion → In Progress

Change abandoned by Daniel Pawlik (<email address hidden>) on branch: master

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