If you are running a remote desktop solution in Azure, you might want to know whether it makes sense to buy licenses for your Remote Desktop Services (RDS). In fact, most of our customers do use RDS CALs in Azure. However, there are some scenarios where you’d rather pay-as-you-use. 

In this blog post, I’m going to walk you through the licensing options for RDS. 

What is RDS? 

Remote Desktop Services (RDS), also known as Terminal Services or Citrix, provides users with access to their applications and data from any device connected to the network. The service allows users to connect to Windows desktops, Mac OS X desktops, Linux desktops, iOS devices, Android devices, and more. It’s an enterprise-class technology that can be used by organizations of all sizes. 

How does RDS work? 

When a user connects to an application on his/her computer, they’re actually connecting to a virtual machine running on Microsoft’s servers. This virtual machine has its own operating system, which runs the application. When the user disconnects, the connection between them and the server ends. 

When a user connects to an app via remote desktop services, he/she doesn’t need to install anything on their local PC. Instead, the app is installed on the virtual machine that is hosting the app. The user then logs into the virtual machine using a client application such as VNC Viewer or LogMeIn Rescue. 

Why would you use RDS? 

There are many reasons why you may choose to use RDS instead of installing apps locally. For example, if you have a large number of employees who need to access multiple apps simultaneously, you’ll save time and money by not having to install each app separately. You could even provide one license per employee, so that everyone gets access to the same apps at once. 

Another reason to consider remote desktop service is when you have a mobile workforce. If you don’t already offer remote access solutions, you can easily integrate RDS into your existing infrastructure. Finally, if you have a BYOD policy, you can allow employees to use their personal devices to access corporate resources. 

Which Licenses should you purchase? 

You can purchase three types of licenses for RDS: 

  • RDS CAL – A single license entitles you to run one instance of RDS. 
  • Site License – A site license is required if you plan to host RDS instances on a physical server. 
  • Virtual Machine Scale Unit (VMSU) – A VMSU license is required if you want to run RDS instances on a cloud computing platform like Azure. 

Let’s look at these options in detail. 


A single CAL is required to run a single instance of RDS. This means that you can only run one RDS session at a time. 

Site Licenses 

A site license is required to run remote desktop service instances in a physical environment. You can scale up and down the number of RDS sessions based on demand. 

Virtual Machines 

A VMSU license enables you to run remote desktop service instances within a virtual machine. Each VM requires a separate license. 

Licensing Options 

If you decide to go with a CAL, you must purchase a Site License. If you decide to go with either a Site License or a VMSU, you must purchase a Virtual Machine Scale Unit (VSU). 

Note: You cannot mix and match CALs and VMSUs. You must purchase a Site License or a Virtual Machine Scale Unit. 

What happens if I exceed my licensing limits? 

If you exceed your CAL limit, you will receive a warning message informing you of this fact. In addition, you will see a message indicating that you are out of CALs. However, you won’t lose any functionality. Your remote desktop service sessions will continue to function normally. 

If you exceed your Site License limit, you will be notified that you are out of Site Licenses. Your RDS sessions still work fine, but you will no longer be able to add additional remote desktop service instances. 

If you exceed both your CAL and Site License limits, you will be notified of this fact. Your RDS sessions stop working completely. 

How do I renew my RDS Licenses? 

To renew your remote desktop service licenses, simply log into the Amazon Web Services console and click Renew Now. 

Do I need to pay for CALs every month? 

No. You only need to pay for CAL licenses when you first create them. After that, they remain active indefinitely. 

Can I change my RDS settings after creating them? 

Yes. You can modify most of the settings associated with an RDS instance. The following table lists all of the available settings. 

Setting Name Description Default Value Allocation Size, the size of the storage volume used to store data for your RDS instance. 5 GB Minimum Provisioned IOPS The minimum provisioned number of I/O operations per second (IOPS) that you request from your database engine.