If you’re going to spend a lot of time learning a particular tool or platform, you want it to pay off. In the context of developer and cloud platforms, though, it’s often difficult to tell which will prove truly profitable in the long term.

The latest edition of Stack Overflow’s annual Developer Survey asked its respondents which technologies paid them the most. When you isolate their answers by platform, you can see that some of the most popular ones (such as Amazon Web Services) also yield the biggest paychecks:

Those salary figures (drawn from 28,873 responses) include salaries, bonuses, and perks before the inevitable taxes and deductions. What can we draw from these rankings?

Colocation is the practice of renting out space within an established datacenter for one’s servers and storage. Colocation saves businesses the effort and expense of maintaining an actual datacenter facility (or an on-premises server area); you rent the rack space and bring your own servers. It’s a complicated enterprise, which is why related skills are in demand (and lucrative).

Meanwhile, AWS remains an intensely lucrative cloud platform—more so than its popular competitors in the space, including Microsoft Azure, Google Cloud, and cloud offerings from Oracle and IBM. Many businesses rely on AWS for pretty much everything cloud-related, a situation that seems likely to change anytime soon. (Microsoft Azure has been gaining ground among customers, though, with Google Cloud coming in third.)

As with so many other things in tech, it all comes down to mastery. If you know the nuances of a platform (and its updates), you’ll be valuable to any organization that relies on that platform in some way. And that, in turn, can lead to significant compensation—especially if the platform is complex, specialized and/or used by only a relatively small number of companies.