Before you can use your Citrix product, you must install Citrix Licensing. Citrix Licensing is a system of components that function together. This system includes:
Every Citrix product environment must have at least one shared or dedicated license server. License servers are computers that are either partly or completely dedicated to storing and managing licenses. Citrix products request licenses from a license server when users attempt to connect.
When users connect to a Citrix product, it draws licenses from the license server. That is, the Citrix product requests to check out a license from the license server on behalf of the user or client device. When the license is successfully checked out, the user can run the product.
Depending on the size and configuration of your product deployment, you may deploy licensing on a server shared with other applications, a dedicated license server, or multiple license servers.
License files must be located on the license server that is associated with the product you are licensing and the product must be configured to communicate with that specific license server. The License Administration Console lets you manage and monitor your Citrix licenses by providing a user interface to the license server. You can view a dashboard of licenses and alerts, import license files, and manage license server settings.
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 4000 continuous connections.
For example, when a server running XenApp 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.
A Citrix product goes through a three-step process to check out licenses:
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, 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 indicates 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.
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. One example of disconnected mode is when a user checks out a Single Sign-on license for a laptop, and then uses the laptop when it is not connected to the server. For products that operate in disconnected mode, the grace period takes effect after the preconfigured time specified for the license check-out expires.
The license server comprises several licensing components:
When a product requests a license from the license server, the Citrix vendor daemon determines whether a license is available for the request.
The license request process has two phases: the product startup phase and the user connection phase.