When configured on Edge DNS, alias zones receive traffic like any other zone and are counted as regular zones from a billing standpoint.

For example, if a Edge DNS contract allows for 50 zones, and 20 regular zones and 30 alias zones are configured, then these 50 zones will be within the contract entitlement. If 5 additional alias zones are configured, then the total of 55 zones will incur a 5 zone overage based on the per-zone overage rate.