This article explains how to register your cloud VDA 

Instructions

1. Before a VDA can be used, it must register (establish communication) with one or more Controllers or Cloud Connectors on the site.
2. The VDA finds a Controller or Connector by checking a list called the ListofDDCs located under registry key "HKLM\Software\Citrix\VitualDesktopAgent".
3. The ListOfDDCs on a VDA contains DNS entries that point that VDA to Controllers or Cloud Connectors on the site. For load balancing, the VDA automatically distributes connections across all Controllers or Cloud Connectors in the list.