Horizon Cloud Service on IBM Cloud establishes zones that segregate the different resources based on their function. Horizon Cloud Service has three zones. Each zone is unique to each Horizon Cloud Service deployment and is not shared.

Zone Description
Security Zone A DMZ where the external Unified Access Gateway appliances reside. It facilitates secure remote access to the Horizon Cloud Service tenant environment.
Services Zone Where Horizon Cloud Service is hosted, including tenant appliances, utility servers, and internal Unified Access Gateway appliances.
Desktop Zone Zone that hosts the desktops and RDSH servers.