Backend API development/communication

I am currently doing backend development with the following objective:

User clicks button on website (frontend), virtual machine is spawned for user (backend). I'm trying to whiteboard the best way to do this. Can someone let me know if my thought process in on the right track.

The part I'm struggling with is how these two communicate/connect with each other, especially if they are on different machines and/or in different programming languages.

My research has led me to believe that building a REST API for my backend application would be the best way to go about this. The front end can send a POST request, which my backend API will receive and do the required spinning up of machines.

My only concern is that every time I read about REST, it is in terms of developing CRUD functionality, or returning datasets, not necessarily executing commands on the server. So I wasn't sure if I was using the REST concept appropriately.

And a picture with some sudo code to help me visualize it.