Ask HN: Resources about back end development?

I have recently needed to write a simple backend for my mobile app side project. I decided try PaaS with app engine and aws. Professionally I do mobile/web frontend most of the time. I've managed to get some basics up and running relatively easy although it was still harder than expected especially with app engine that seemed to have lacking documentation. At this point I have found it hard to find solid resources about how to move from 'hello world' level of simple API examples to a solid product. I would appreciate any recommendations for books/articles/courses. I'm mostly interested in security & scalability. Thanks.