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About this interview
A technical interview on Scalability Fundamentals & Back-of-Envelope Reasoning, pitched at the easy level. A voice AI interviewer leads the conversation, adapts its questions to your answers, keeps you on topic, and afterward gives you honest, specific feedback on where you were strong and where to improve. Expect roughly 30 minutes.
What you'll be assessed on
Estimate throughput, storage, and bandwidth requirements from first principles using back-of-envelope math
Explain the role of DNS, CDN, load balancers, and caches in a horizontally-scaled web service
Distinguish stateless from stateful tiers and articulate why statelessness enables horizontal scaling
Describe database read replicas, write-ahead logs, and when to shard vs. replicate
Topics covered
Single-server limitsScaling dimensionsLoad balancersPowers of two and data unitsCDNQPS estimationStateless web tierCaching patternsDatabase replicationWrite-ahead logStorage estimationCDN cache miss flowFault toleranceLatency numbers
A few sample questions
Just examples to set expectations - the real interview has many more and adapts to your responses.
“When a startup first launches, it often runs everything — web server, database, and cache — on a single machine. Walk me through why that works initially and what breaks first as traffic grows.
“Describe the latency order of magnitude differences between an L1 cache read, a main memory read, a sequential disk read, and a network round-trip within a data center. Why do these numbers matter when designing a system?
“What is a reverse proxy and how does it differ from a load balancer? What additional responsibilities can a reverse proxy take on besides distributing traffic?