For a single-user migration, you do not require additional Microsoft licenses. However, if you want to build a multi-user environment (via oneclick™ Cloud Resource Manager or via a connections to RDS servers), you must have a valid license for Microsoft Windows Remote Desktop Services.
Depending on the type of delivery, there are different licensing options for Microsoft Windows Server:
Delivery from our own data center (On-Premises)
For this purpose you need a “Microsoft RDS Client Access Licenses” (RDS CAL)*.
Delivery from a hosted data center (Private, Public)
For this purpose, you can use a “Microsoft RDS Client Access Licenses” (RDS CAL)* with active “Microsoft Software Assurance” (SA).
Alternatively, you can use a “Microsoft RDS Subscriber Access Licenses” (RDS SAL) from the Microsoft SPLA License Program as part of a monthly billing.
It depends on your cloud provider whether you need to license Microsoft RDS SAL yourself or whether the license is included in the cost of use.
Very often, it is assumed that no RDS licensing is required when accessing the desktop of a Windows server or applications installed on that desktop via a third party solution such as oneclick™. That’s wrong! Microsoft Windows Remote Desktop Services licensing is required when a Microsoft Windows Server Desktop or applications deployed through a Microsoft Windows Server Desktop can be accessed. It is irrelevant whether Microsoft Remote Desktop Services or any other technology is used.
*Microsoft RDS CAL can be licensed per user or per device. In most cases, user licensing is the best option.