I will never walk into a backend interview without solving these 20 questions.

Most people study for backend interviews by reading system design books and trying to memorize architectures. They learn to draw boxes labeled Database and Cache. That approach gets you through the initial screening. It falls apart as soon as the interviewer asks a follow up question about what happens inside those boxes when traffic spikes. I compiled this list based on the questions that actually get asked in real rooms. I failed many interviews because I did not know the answers to these. I a