I didn't feel much difficulty in answering their questions. Probably this is my first company where i have answered all questions with confidence in which i didn't select. It is a big surprise and unfortunately they won't reveal the reasons for not shortlisting... Questions are similar what have posted in this website. Just look at the AWS case studies. Their questions covers 40% of their case studies. You don't need AWS knowledge. But you need to answer how cloud works and best practices in deploying web applications for higher scalability, performance and network latency point of view. If you didn't worked on AWS then tell them upfront your strengths. They didn't ask me any AWS products as i didn't work on it. But they have asked me all cloud questions in which i worked for(VMWare/Azure/Rackspace/etc).