Building a redundant Citrix environment requires a bit of thought and understanding of the different components. This is a high level review of what needs to be addressed when building High Availability into your XenDesktop 7.x design.
NetScaler Gateway. This is the first point of contact for remote users. If NetScaler is down, remote users will not be able to access and authenticate to the NetScaler Gateway which means no access for them. So at least dual NetScalers are needed to eliminate Single Point of Failure.
StoreFront. This is where the applications and desktops are enumerated for users that need to access them.Again redundancy is needed, at least a pair of StoreFront servers is needed.
Deliver Controller. Once users have successfully authenticated, StoreFront contacts the Delivery Controller to get a list of available resources (desktops/applications). So again N+1 redundancy is needed for the delivery controller.
Database Delivery Controllers require Database (Microsoft SQL). Now remember under the new FMA architecture, Local Host Cache feature is no longer availablein XenDesktop 7.x. So High Availability for the Database is required. Here you have a few options for High Availability. Citrix recommended option is mirroring. Why? Because the fail over is almost instant. With that said, Microsoft is planning on removing Mirroring from future SQL releases! There are other options for Database High Availability such as Clustering, High Availability on Hypervisor level, or AlwaysOn Availability Groups.
Provisioning Services (PVS) server. Delivery Controller have 2 connections available: Connections to the Hypervisor (MCS) and connections to PVS server. If using PVS and PVS server is not available when a client boots, then the users will not be able to access the content they need. A minimum of two PVS servers should be the minimum implemented per site.
Shared Storage. PVS needs shared storage to access boot image and vDisk. Now most likely that shared storage will be located on a highly available SAN connected to the PVS servers.
Hpervisor. You will need N+1 for redundancy on the infrastructure level as well. Also keep in mind if using MCS, those connections between the Delivery Controllers and Hypervisors will need to have redundancy built in as well.
License Server. You have one last Citrix component here which is the Citrix License Server. That is the only ccomponentyou do not need to have redundancy for. Why? Because it has 30 days grace period so even with license server down, the environment will still function. What happens if 30 days pass? If your environment is still down after 30 days, then frankly you have more serious issues to worry about!
So is that it?
Yes .. well almost. As far as Citrix components are concerned you have redundancy built in. However, there are other components you have to consider that Citrix environment depends on.
Domain Controller. Without a domain controller, your users will not be able to authenticate, therefore unable to access Citrix environment. N+1 is a given for your DCs.
DHCP server. This is needed for IP address assignment
DNS server. This is needed for name resolution.
This was a high level review of building redundancy into XenDesktop 7.x design
Thank you for reading.