The problem with your question is that they are there to show off their knowledge. I failed a tech interview once, question was build a web page/back end/db that allows people to order let's say widgets, that will scale huge. I went the simpleton answer route, all you need is Rails, a redis cache and an AWS provisioned relational DB, solve the big problems later if you get there sort of thing. Turns out they wanted to hear all about microservices and sharding.