Technical overview

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:

License server. A system that allows licenses to be shared across the network.

License files. The files required to license your product. These files are stored on the License Server.

Citrix Licensing Manager. The recommended License Server management method that enables the following:

  • Exporting license use data for use in reporting.
  • Configure the user and group access to manage the License Server.
  • Installation of licenses by using the license access code or a license file (.lic).
  • Enable and disable the supplemental grace period.
  • Modify these ports:
    • License Server (default 27000)
    • Vendor Daemon (default 7279)
    • Web Services for Licensing (default 8083)
  • Display details of licenses after they are installed using a license access code or downloaded file.
  • Configuration of Customer Experience Improvement Program (CEIP) and Call Home.
  • Retry failed usage statistic uploads to Citrix.
  • Automatically or manually checks for Customer Success Services renewal licenses and notifies you or installs the licenses if found.
  • Configure historical use data retention period. Default data retention period is 180 days.
  • Notifies you of the License Server state - Missing startup license, time issues, uploader failures.

License Administration Console. Another interface you can use to manage your license files and your License Server.

Web Services for Licensing. Enables Studio, Director, and the Licensing Administration PowerShell Snap-in to:

  • Communicate with the License Server and manage users.
  • Allocate and install licenses.
  • Display License Server health, license usage, and other alert messages.

Citrix License Management Service. Enables management of your license environment through a license management console within Citrix Insight Services. This service assists with license management and support:

  • Allocating new licenses if you are about to exceed your license capacity
  • Rescinding old licenses after an upgrade
  • Managing duplicate licenses in a Disaster Recovery (DR) environment

Product-side settings in your Citrix products that are associated with the License Server.

For more information, see Licensing elements and Services.

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. Some Citrix products check out the license when 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.

For example, when a server running Citrix Virtual Desktops requests a license, the product retrieves the License Server name and port number information from the data store. The product then establishes a connection to acquire the appropriate licenses.

Note

When configuring the product-side setting for the License Server name, do not use localhost. Though you can use the host name, IP address, or FQDN instead, Citrix recommends that you use the FQDN.

There are three stages of the license checkout process.

checkout-process

A Citrix product goes through a three-step process to check out licenses:

  1. At startup, a computer running a Citrix product checks out a startup license.
  2. A client device connects to the product server.
  3. The product requests a license from the License Server.

Citrix products, such as Citrix Virtual Desktops, 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. During the grace period, the product uses its local record of the licenses to continue licensing the product. Citrix products update this record every hour.

Scalability

This section provides guidance to ensure successful License Server usage by examining the impact of license usage scalability in a Citrix environment. We performed the following scalability testing:

Virtual Machine Hardware/Configuration: Intel Xeon E5-2650 v3 @ 2.30 GHz 4 Virtual CPUs 8 GB RAM Windows Server 2016

6.5 and earlier Concurrent:

  • 3000 connected Citrix Virtual Apps servers
  • 53,000 concurrent licenses
  • 50–60 connections per second

Efforts to scale more than 53,000 licenses result in servers going into a grace period. Also, there are issues with WMI, lmstat, and the License Administration Console. We recommend that you maintain 50,000 or fewer concurrent connections per License Server.

7.x Concurrent:

  • 16 Delivery Controllers
  • 70,000 concurrent licenses
  • 50–60 checkouts per second

7.x User/Device:

  • 16 Delivery Controllers
  • 150,000 User/Device licenses
  • 50/60 checkouts per second

CITRIX.exe is a single threaded process. While serving Concurrent connections, the maximum connection limit is based on single core processor speed. During peak activity, CITRIX.exe uses 100% of a single core and eventually starts timing out. This usage might cause Citrix products to go into a grace period or errors in the License Administration Console or other License Server utilities. After the License Server has processed backlog connections, it returns to normal. Monitor CITRIX.exe processor usage to determine if a faster processor is required. We recommend if you experience issues in high scalability environments, you deploy more License Servers.

User/Device technology is multi-threaded and scales better than Concurrent. During license optimizations, you might see that periods were licensing activity takes 100% of a single core. This usage is normal and doesn’t impact CITRIX.exe processor usage or functionality. We recommend that you monitor License Server resource usage and add more License Servers to maintain a properly functioning environment.

We recommend that you specify thread use to improve performance. For more information, see Improve performance by specifying thread use.

Note

Running WMI, lmstat, lmutil, or other inventory actions can negatively impact License Server performance. We recommend that you minimize these activities. If you require usage data, export the data from the Citrix Licensing Manager. For more information, see Historical usage.

Grace period

If product servers lose communication with the License Server, the users and the products are protected by a grace period. The grace period allows the product servers to continue operations as if they were still in communication with the License Server. After the Citrix product checks out a startup license, the product and the License Server exchange “heartbeat” messages every five minutes. The heartbeat indicates to each that they are still up and running. If the product and the License Server don’t send or receive heartbeats, the product lapses into the licensing grace period and licenses itself through cached information.

Citrix sets the grace period. 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.

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.

Supplemental grace period

For the supplemental grace period to be available, you must use a minimum of XenApp 7.6 or XenDesktop 7.6.

If all licenses are in use, supplemental grace period enables unlimited connections to a product, allowing you to understand and address the issue. This period lasts until 15 days elapses or you install more retail licenses, whichever comes first. We recommend that after the supplemental grace period starts, you allow it to run out rather than adding licenses immediately to clear the warning condition.

After the period expires, normal connection limits are enforced. Users are not disconnected. As they disconnect, no new connections can occur until license levels return to normal.

After the supplemental grace period completes, it isn’t automatically re-enabled. To re-enable the supplemental grace period, install another retail license, and then normal license limits are enforced. When you re-enable the supplemental grace period by installing the new retail license, a new 15-day supplemental grace period starts the next time you exceed maximum installed licenses.

Note

If you install licenses while the supplemental grace period is in force, the License Server exits the supplemental grace period. Reenabling the supplemental grace period before determining the reason for the supplemental grace period might cause you to reenter the period after installing new licenses.

Supplemental grace periods are granted per product version and edition and only for retail licenses. The supplemental grace period is enabled by default when you first install licenses. To configure the supplemental grace period, use the Citrix Licensing Manager.

Supplemental Grace Period example

If you have a maximum count of 1000 licenses installed, and you make another connection (maximum licenses + 1), the supplemental grace period starts. You then have a temporary, 15-day period giving you extra capacity to deal with unforeseen capacity issues.

Important

The supplemental grace period and license overdraft are two different features. The supplemental grace period is a feature of the product and the License Server. License overdraft is a feature of the license. For information about license overdraft, see License overdraft.