Citrix makes use of SQL Server AlwaysOn, mirroring or clustering abilities within SQL and clustering at the Hypervisor level to ensure that Delivery Controllers have a constant connection to the SQL site database. Citrix Connection Leasing in XenApp/XenDesktop 7.6+ pushes the availability further ensuring that if in the event the database is innaccessible, users most recent connections to desktops and applications are cached on Delivery Controllers and connections can continue to be brokered. Keep Reading