I'm working on a list of filters ordered by cost. This is what I have so far. Does this look reasonably correct for Rocky?
Cheap Filters:
AllHostsFilter - does no filtering. It passes all the available hosts. AvailabilityZoneFilter - filters hosts by availability zone. AggregateInstanceExtraSpecsFilter - checks aggregate metadata set with aggregate_instance_extra_specs. All hosts are passed if no extra_specs are specified. AggregateCoreFilter - filters hosts by CPU core number with per-aggregate cpu_allocation_ratio setting. AggregateRamFilter - filters hosts by RAM with per-aggregate ram_allocation_ratio setting. AggregateDiskFilter - filters hosts by disk allocation with per-aggregate disk_allocation_ratio setting. AggregateNumInstancesFilter - filters hosts by number of instances with per-aggregate max_instances_per_host setting. AggregateIoOpsFilter - filters hosts by I/O operations with per-aggregate max_io_ops_per_host setting. AggregateMultiTenancyIsolation - isolate tenants in specific aggregates. AggregateTypeAffinityFilter - limits instance_type by aggregate. AggregateImagePropertiesIsolation - isolates hosts based on image properties and aggregate metadata. DifferentHostFilter - allows the instance on a different host from a set of instances. SameHostFilter - puts the instance on the same host as another instance in a set of instances. ComputeFilter - passes all hosts that are operational and enabled. NumInstancesFilter - filters compute nodes by number of running instances. IoOpsFilter - filters hosts by concurrent I/O operations.
More Expensive Filters:
ServerGroupAntiAffinityFilter - This filter implements anti-affinity for a server group. ServerGroupAffinityFilter - This filter works the same way as ServerGroupAntiAffinityFilter. The difference is that when you create the server group, you should specify a policy of 'affinity'. ImagePropertiesFilter - filters hosts based on properties defined on the instance's image. Doc on setting image properties is here: https://docs.openstack.org/glance/rocky/admin/useful-image-properties.html IsolatedHostsFilter - filter based on isolated_images, isolated_hosts and restrict_isolated_hosts_to_isolated_images flags. SimpleCIDRAffinityFilter - allows a new instance on a host within the same IP block. MetricsFilter - filters hosts based on metrics weight_setting.
Most Expensive Filters:
PciPassthroughFilter - Filter that schedules instances on a host if the host has devices to meet the device requests in the 'extra_specs' for the flavor. ComputeCapabilitiesFilter - checks that the capabilities provided by the host compute service satisfy any extra specifications associated with the instance type. NUMATopologyFilter - filters hosts based on the NUMA topology requested by the instance, if any. JsonFilter - allows simple JSON-based grammar for selecting hosts.
Deprecated Filters:
Please don't use any of these; they are obsolete in Rocky:
RetryFilter - filters hosts that have already been attempted for scheduling. Obsolete since Queens. RamFilter - filters hosts by their RAM. Obsolete since Pike. CoreFilter - filters based on CPU core utilization. Obsolete since Pike. DiskFilter - filters hosts by their disk allocation. Obsolete since Pike.