Maybe at the entry level but what about scaling an application that handles personal info (and credit cards) over multiple servers (just for example)? What's t

Maybe at the entry level but what about scaling an application that handles personal info (and credit cards) over multiple servers (just for example)? What's the most complex backend stuff you can think of? Perhaps Google or Amazon level engineering? There's simply no equivalent of that on the front end. TL;DR I'm pretty sure the majority of the PhD's at Google are not writing CSS.