Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/schedule-set-availability-zones.

Description:

I updated the description of this blueprint because previously generated a lot of confusion about the goal.


The goal of this blueprint is to have multiple schedule availability zones as default instead only one.
This means:
deprecate "default_schedule_zone" configuration option and have instead "default_schedule_zones=[]"

When an instance is created, if the user doesn't define an availability zone, it will be schedule into one node in the list of default schedule availability zones.
The advantage of this aproach is when an deployment has multiple availability zones the instances will be spread between them instead overload only one, if users don't specify an availability zone.


Implementation:
- deprecate "default_schedule_zone" and create "default_schedule_zones" option.
- if default_schedule_zone is present in configuration use this value to not break current configurations (default_schedule_zones=[default_schedule_zone])
- if an user doesn't specify an availability zone it shouldn't be added in the DB (remove the current behaviour). Anyway when query for the avz of an instance nova doesn't use this value.
- change AvailabilityZoneFilter to support multiple default azs.


Specification URL (additional information):

None