You are really talking about building an OpenStackcloud. An Availability zone contains all the controller nodes and services that orchestrate the cloud, nova, glance, cinder, keystone and the like. You can take an availability zone and slice it into aggregates and there is an api for creating aggregates. Also there is good link below.

nova aggregate-create test-aggregate2 test-az
+----+-----------------+-------------------+-------+----------+
| Id | Name | Availability Zone | Hosts | Metadata |
+----+-----------------+-------------------+-------+----------+
| 2 | test-aggregate2 | test-az | | |
+----+-----------------+-------------------+-------+----------+

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