How do you scale a frontend application to a million users ? (opens in new tab)

I was recently in a job interview (yes, the kind you have to do when you get laid off) and the interviewer asked me: "How would you scale a frontend application from 100,000 users to a million plus?" I gave a decent enough answer at the moment. But afterwards, I kept thinking about everything I didn't say. So here we are. Consider this my full answer, delivered about three months too late to actually matter for that job. First, Let's Calibrate Scaling a frontend isn't just about throwing more...