The System Design Fundamentals That Actually Get Tested
Interviewers aren't scoring diagram complexity — they're testing a small set of fundamentals and your ability to reason through trade-offs.
I used to think system design was about drawing the most complex diagram possible. Mock interviews taught me otherwise: interviewers are checking whether you deeply understand a small set of fundamentals, and whether you can justify trade-offs when you combine them.
The list that actually gets tested
Across most system design questions, the same building blocks show up over and over:
- Scalability basics
- Load balancing
- Caching
- Database choices — SQL vs NoSQL, replication
- Sharding and partitioning
- Message queues
- CAP theorem
None of these are new or fancy.
What actually separates candidates
Being able to explain each of these clearly, and combine two or three of them to solve a real problem, is basically the whole interview. It's not about knowing more acronyms than the next person — it's about reasoning from a small toolkit to a coherent design under constraints you didn't choose.