This is a classic "Systems Design" interview question. There are lots of resources available to prepare for it. This question isn't testing your knowledge of AWS, it's testing your ability to plan and design a large software system around specific constraints. More on reddit.com

what have you done in AWS? AWS has a free tier. Sign up. You get 700+ hours to run an instance. That's enough to run one instance all month. Don't do that. Practice orchestrating multiple instances. Practice fail-over. Practice config management like Ansible/Chef/Puppet. Practice making the root drive disposable, and only putting data on a backed-up EBS data drive. Practice creating AMIs. Find some projects in Lambda on github and practice installing, configuring and monitoring them. Use SES. Use S3 lifecycle rules. Understand IAM roles. Stop using the Console - You should use the AWS CLI for everything, it's much more efficient and repeatable. Try managing some things using TerraForm. Make a website with GeoIP, CDN, where it takes markdown documents from one S3 bucket and transforms them into HTML via Lamba to another bucket. Yes, this takes time. But it won't cost more than a few bucks. More on reddit.com

Ensure the SigningCertURL is from a trusted AWS domain (for example, https://sns.us-east-1.amazonaws.com ). Reject any URLs outside AWS domains for security reasons. Guess this is left up to the reader to implement. More on reddit.com

My previous experience would call these "stump the dummy" questions, and I absolutely hate them. Instead of trying to have them spit out a trivia answer, you should ask a conceptual question related to DevOps. Stuff like How would approach troubleshooting a slow connection within the application? How would you build a while ensuring reliability and the ability to capture failures/errors? They can ask clarifying questions, but they need to form their knowledge into a coherent and sensible answer. I believe these types of open-ended questions give a better indicator of experience and wisdom than a trivia question. Just stay away from questions that start with "what is ...?" as you might only get a single word answer that doesn't give you insight into the candidates thought process or breadth of knowledge. More on reddit.com