Instances can now be created in preferred cells. Previously, the cell scheduler would select a destination at random from known cells. Filters and weights can now be defined by administrators to direct builds to a particular cell. The keys scheduler_filter_classes and scheduler_filter_classes are configured under the cells group in nova.conf. The new weights and filters available: ram_by_instance_type: Select cells with the most capacity for the instance type being requested. weight_offset: Modifies the DB to weight a particular cell. Also useful for disabling a cell. mute_child: Assigns negative weight to cells that have not sent an update to their parent cell. target_cell: Specifies a scheduler.