Open source is completely welcome in Windows Azure!
One of the most amazing things about working in the Azure space is how open we are to people who want to use Azure, but don’t want to use .NET. Not only do we allow our Azure customers to use whatever language/environment they want, we even go so far as to publish SDKs for some of the most popular languages! Check out the current list below:’
Node.js - https://www.windowsazure.com/en-us/develop/nodejs/
Java - https://www.windowsazure.com/en-us/develop/java/
PHP - https://www.windowsazure.com/en-us/develop/php/
Python - https://www.windowsazure.com/en-us/develop/python/
Ruby - https://www.windowsazure.com/en-us/develop/ruby/
We even ship an Eclipse plug-in!
https://msdn.microsoft.com/en-us/library/windowsazure/hh694271.aspx