Scenario: A Citrix Engineer is administering a Citrix Virtual Apps and Desktops environment consisting of multiple zones, including a Primary zone…

The scenario describes a failure of the single Delivery Controller in the Primary zone, which prevented Virtual Delivery Agents (VDAs) within that same zone from registering. In a Citrix Virtual Apps and Desktops multi-zone architecture, VDAs register with Delivery Controllers located within their own zone. To resolve the single point of failure and ensure high availability for VDA registration specifically within the Primary zone, a second Delivery Controller must be added to that zone. This provides redundancy, allowing VDAs to register with the alternate Controller if the first one becomes unavailable, directly preventing a recurrence of the described outage with the most targeted and minimal effort.

B. one of the Satellite zones: Adding a Controller to a Satellite zone provides redundancy for that zone only; it does not resolve the single point of failure in the Primary zone.
C. the Primary zone and both Satellite zones: While adding Controllers to all zones is a best practice for overall site resilience, it exceeds the "minimal administrative effort" required to fix the specific problem described.
D. both Satellite zones, but NOT the Primary zone: This option completely fails to address the root cause of the outage, leaving the Primary zone vulnerable to the exact same failure.

1. Citrix Virtual Apps and Desktops Product Documentation, "Zones": "For high availability, we recommend that each zone has at least two Controllers. Because sessions can be brokered across zones, the Controllers in one zone can fail over to Controllers in other zones if needed." More importantly, for VDA registration, it is stated: "A VDA in a satellite zone will never attempt to register with a Controller in the primary zone." This establishes the principle that VDA registration is zone-specific, meaning Primary zone VDAs register with Primary zone Controllers.

Source: Citrix Virtual Apps and Desktops 7 1912 LTSR documentation, Manage > Zones section.

2. Citrix Tech Zone, "Design Decision: Sizing and Scalability": This resource emphasizes the importance of N+1 redundancy for critical components like Delivery Controllers within a zone to ensure service availability. "For each zone, it is recommended to have at least two Delivery Controllers for redundancy."

Source: Citrix Tech Zone, CVAD Reference Architecture, Design Decision: Sizing and Scalability.

3. Citrix Virtual Apps and Desktops Product Documentation, "Local Host Cache": The documentation on Local Host Cache (LHC) explains that Controllers in a Satellite zone use LHC when they cannot contact the site database in the Primary zone. This reinforces the architectural separation and the need for intra-zone redundancy, as inter-zone failover for VDA registration is not the primary mechanism. The failure described was a Controller failure, not a database connection failure, making local Controller redundancy the direct solution.

Source: Citrix Virtual Apps and Desktops 7 1912 LTSR documentation, Manage > Local Host Cache section.