What is the correct method in Linux on Azure to test if you are an Azure VM ?

Hello 

for Amazon 

At the moment I can test if I am in EC2 or physical fairly simply by using Curl against instance metadata, 

how can I tell if I am in Azure VM in Linux ? Is there some probe in WAAGent test that guarantees I am in Azure and not, for example, Hyper-V ? 

Thanks

C.