Licensing is always a complex discussion with SQL Server. Depending on the way you run it, the edition, the version, whether you've purchased Software Assurance, and more, you might struggle to ensure you are in compliance with Microsoft's terms.
This can be even more complex when you move to the cloud, as sometimes your setup could include a license, and sometimes it doesn't. If you lift-and-shift to cloud VMs, Azure lets you bring your existing licenses with the Azure Hybrid Benefit, which is tempting for organizations that want to get out of the data center business and move their workload to the cloud.
However, that isn't necessarily the same for all clouds. While Amazon lists various ways you can bring your licenses to AWS, Microsoft hasn't felt that was legal. They've noted in 2019 that their "cloud partners" couldn't support workloads on non-SA licenses. I can't quite determine if SA licenses can be used, as lots of information out there is conflicting. Microsoft's FAQ seems to support the idea that you need dedicated hosts, not just any shared VM.
Not all cloud providers count, however. This week Microsoft noted that some cloud providers can let you run your workload by bringing your licenses. These are smaller providers in Europe who filed complaints. Likely these providers can't offer the scale or pricing of GCP, AWS or Alibaba, so they aren't as big a revenue threat as these providers.
I don't know what I think is the right thing, as once I've purchased a license, why does the location or ownership of the VM count? I ought to be able to run the software within the same guidelines in Rackspace, EC2 or GCP just as I would on-premises. However, such is the strange world of software licensing.
If you deal with licensing, I'm sorry, but also, you should note that there are rules and restrictions when you move to the cloud. That's something I see increasingly happening in many organizations, so educate yourself so that you can make the right recommendation. And when you get ready to purchase licenses, think about how SA not only affects upgrades, but also the flexibility of migration.