A zone is a configurable grouping of XenApp servers. All farms have at
least one zone. All servers must belong to a zone. Unless otherwise specified
during XenApp Setup, all servers in the farm belong to the same zone, which is
Zones have two purposes:
- Collect data from member
servers in a hierarchical structure
- Efficiently distribute
changes to all servers in the farm
Each zone contains a server designated as its data collector. Data
collectors store information about the zone’s servers and published
applications. In farms with more than one zone, data collectors also act as
communication gateways between zones.
This illustration depicts a server farm with multiple zones. Each
zone’s data collector communicates with the other data collectors across the
Because session and load information within a XenApp farm can become
large in enterprise deployments—up to several megabytes—to ensure a scalable
and resilient XenApp farm, it is imperative that you design zones based on your
XenApp member servers replicate their dynamic data to the ZDC
designated for their zone. XenApp uses a star topology for replication among
zones—each ZDC replicates all of its zone dynamic data to all other ZDCs in the
farm. Thus, it is important to design zones so that there is adequate bandwidth
When designing zones, the most important variables to consider are
latency and bandwidth. The amount of bandwidth and the impacts of latency are
highly dependent on your XenApp deployment. The lower the bandwidth and the
higher the latency, the longer a farm takes to resynchronize the dynamic data
among zones after an election.
In farms distributed across WANs, zones enhance performance by
grouping geographically related servers together. Citrix does not recommend
having more than one zone in a farm unless it has servers in geographically
distributed sites. Zones are not necessary to divide large numbers of servers.
There are 1000-server farms that have only one zone.
Data collectors generate a lot of network traffic because they
communicate with each other constantly:
- Each zone data collector
has an open connection to all data collectors in the farm.
- During a zone update,
member servers update the data collector with any requests and changed data.
- Data collectors relay
changes to the other data collectors. Consequently, data collectors have the
session information for all zones.
In general, Citrix recommends using the fewest number of zones
possible, with one being optimal. If all farm servers are in one location,
configuring only one zone for the farm does not reduce performance or make the
farm harder to manage. However, in large networks, such as organizations with
data centers on different continents, grouping geographically-related servers
in zones can improve farm performance.
Keep in mind that data collectors must replicate changes to all other
data collectors in the farm. Also, bandwidth consumption and network traffic
increase with the number of zones.
Separate zones are not required for remote sites, even ones on
separate continents; latency is the biggest factor in determining if servers
should be put in their own zone. For large farms with servers in different
geographic regions, create zones based on the location of significant numbers
Also decide if you want to configure failover zones or preferred
zones. If a zone fails, you can configure for user connections to be redirected
to another zone (failover) or control to which zones specific users connect
(preference). Failover requirements might determine the number of zones
For example, an organization with 20 farm servers in London, 50
servers in New York, and three servers in Sydney could create two or three
zones. If the Sydney location has good connectivity to either New York or
London, Citrix recommends grouping Sydney with the larger location. Conversely,
if the WAN connection between Sydney and the other locations is poor, and zone
preference and failover is required, Citrix recommends configuring three zones.
Consider these zone design guidelines:
- Minimize the number of
zones in your farm.
- Create zones for major
datacenters in different geographic regions.
- If a site has a small
number of servers, group that site in a larger site’s zone.
- If your organization has
branch offices with low bandwidth or unreliable connectivity, do not place
those branch offices in their own zone. Instead, group them with other sites
with which they have the best connectivity. When combined with other zones,
this might form a hub-and-spoke zone configuration.
- If you have more than five
sites, group the smaller sites with the larger zones. Citrix does not recommend
exceeding five zones.