In designate we have a pluggable scheduler filter interface.

You can set an ordered list of filters to run on each zone create api
request.

We provide a few basic filters below, and creating custom filters
follows a similar pattern to schedulers.

You can create your own by extending designate.scheduler.filters.base.Filter and
registering a new entry point in the
designate.scheduler.filters namespace like so in your
setup.cfg file:

[entry_points]
designate.scheduler.filters =
my_custom_filter = my_extension.filters.my_custom_filter:MyCustomFilter

The new filter can be added to the scheduler_filters
list in the [service:central] section like so:

[service:central]

scheduler_filters = attribute, pool_id_attribute, fallback, random, my_custom_filter

The filters list is ran from left to right, so if the list is set
to:

[service:central]

scheduler_filters = attribute, random

There will be two filters ran, the designate.scheduler.filters.attribute_filter.AttributeFilter
followed by designate.scheduler.filters.random_filter.RandomFilter

Default Provided Filters

Base Class – Filter

Attribute Filter

Pool ID Attribute Filter

Random Filter

Fallback Filter

Default Pool Filter

In Doubt Default Pool Filter