Licensing operations overview
Typically, the first time a user connects to a Citrix product, the product requests a license from the License Server. When the License Server grants a license request, the Citrix product reserves a license for its use. Reserving licenses for this purpose is known as checking out licenses. When the user logs off from the product server, the product returns the license to the License Server. This process is known as checking in licenses. With some Citrix products the license is checked out as soon as a user connects to the product, and the license remains checked out for a predetermined amount of time.
Each time a Citrix product starts, it opens a connection to the License Server by checking out the startup license. The startup license is a Citrix system file that enables Citrix products to maintain a continuous connection to the License Server. The following figure shows that each product forms its own constant connection to the License Server.
The Citrix product makes a continuous connection to the License Server. The License Server can support up to 10,000 continuous connections.
For example, when a server running XenDesktop requests a license, the product retrieves the License Server name and port number information from the data store and establishes a connection to acquire the appropriate licenses.
There are three stages of the license checkout process.
A Citrix product goes through a three-step process to check out licenses:
- At startup, a computer running a Citrix product checks out a startup license.
- A client device connects to the product server.
- The product requests a license from the License Server.
Citrix products, such as XenDesktop, store a replica of the licensing information from the License Server, including the number and type of licenses. If a Citrix product server loses its connection to the License Server, or the License Server does not respond in a timely manner, the product enters a grace period and uses its local record of the licenses to continue licensing the product during the grace period. Citrix products update this record every hour.
If product servers lose communication with the License Server, the users and the products are protected by a grace period that allows the product servers to continue operations as if they were still in communication with the License Server. After a startup license is checked out by the Citrix product, the product and the License Server exchange "heartbeat" messages every five minutes to indicate to each other that they are still up and running. If the product and the License Server fail to send or receive heartbeats, the product lapses into the licensing grace period and licenses itself through cached information.
The grace period is set by Citrix. It is typically 30 days but can vary depending upon the product. The Windows Event Log, and other in-product messages, indicate if the product has entered the grace period, the number of hours remaining in the grace period. If the grace period runs out, the product stops accepting connections. After communication is re-established between the product and the License Server, the grace period is reset.
The grace period takes place only if the product has successfully communicated with the License Server at least once.
Note: For products that operate in disconnected mode, the grace period takes effect after the preconfigured time specified for the license check-out expires.
Grace period example — two sites, both using the same License Server
The connection between Site 1 and the License Server goes down causing Site 1 to go into the grace period, continuing operation and making connections. For Concurrent licenses, they can connect up to the maximum concurrent licenses installed. For User/Device licenses, they have unlimited connections. When Site 1 reestablishes communication with the License Server, connections are reconciled and no new connections are allowed until they are within normal license limits. Site2 is unaffected and operates as normal.
If the License Server goes down, both sites go into the grace period. Each site allows up to the maximum number of licenses installed. As above, the User/Device licenses have no limit.
Some Citrix products can operate in a disconnected mode (not connected to the server). These products allow a user to check out a license and operate the product for a preconfigured period of time that is set by the administrator. In this case, heartbeat messages are not exchanged. For products that operate in disconnected mode, the grace period takes effect after the preconfigured time specified for the license check-out expires.
Supplemental grace period
For the supplemental grace period to be available, you must be using XenApp 7.6 or XenDesktop 7.6.
License Server VPX does not support supplemental grace periods.
If all licenses are in use, the supplemental grace period enables users to connect to a product for a limited period of time allowing you to address the issue. The default supplemental grace period is 15 days. During this period there is no limit on connections. After it expires, normal (to the extent of license availability) connection limits are enforced. Users are not disconnected, but as they disconnect, no new connections occur until license levels return to normal.
Supplemental grace periods are granted per product and edition and per Subscription Advantage Eligibility date (per product) and only for Retail licenses. For example, if you have two clients requesting XenDesktop Enterprise Concurrent, with different Subscription Advantage Eligibility dates, two supplemental grace periods are granted.
Rearming the supplemental grace period — When you take corrective action (for example, installing an additional Retail license), the supplemental grace period is rearmed, and normal license limits are enforced again. If you take action while the supplemental grace period is in force, the License Server exits the supplemental grace period before rearming. When the supplemental grace period is rearmed, you can trigger a new 15 day supplemental grace period the next time you go over the license limit.
The supplemental grace period is enabled by default. To disable it, enter the following line in the options file: