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Azure services run on [customized] Hyper-V, thus Windows Server.

Azure networking is Linux.

EDIT: Marvel at the NT4 style Task Manager [0].

Microsoft just upstreamed support for running Linux as the Hyper-V equivalent of Dom0, so no Windows required.

That is still a very long way until Azure Host OS gets replaced.

Guessing some of Azure networking (or storage controllers) might even be BSD based ?

Azure networking is Microsoft's own Linux: Azure Linux [0]. I don't know what they use for storage controllers.