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

Azure networking is Linux.

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

[0] https://techcommunity.microsoft.com/blog/windowsosplatform/a...

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

https://www.phoronix.com/news/Linux-6.19-Improves-Hyper-V

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.

[0] https://en.wikipedia.org/wiki/Azure_Linux