Today (June 2020), parts of PlayFab are hosted in Azure and parts are hosted in AWS (legacy, from before the Microsoft acquisition of PlayFab). New features (like our updated server hosting and Party features) are all in Azure. We are in the process of moving the remaining components from AWS into Azure, but we've been very careful and deliberate about this, as we cannot allow any downtime or errors at any point in this process. All changes in this process are a "hot swap", so that you, as a developer with titles running in PlayFab, don't see any difference, or any interruptions.
But that said, why do you ask? Our goal is to make sure we provide the services you need, that they are highly reliable and scalable, that they're white-labelled so that it's you that owns the player relationship, and that they're as inexpensive as possible. If we accomplish that, I'm not sure why it would matter to you.
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