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System Design Interview Questions
Scale, caching and traffic control — design decisions and the math behind them.
3 of 3 questions
Topic
Difficulty
Frequency
Round
Type
IntermediateAsked very oftenScalabilitySystem design · Design
Design a URL shortener at scale
A read-dominated system whose entire design funnels into one decision: how to generate tiny, unique keys — random ones are unguessable, while counter and Snowflake IDs stay unpredictable only if the sequence state stays secret.
url-shortenerscalabilitycaching
IntermediateAsked very oftenTrafficSystem design · Design
Design a distributed rate limiter
A rate limiter is a distributed race: pick an algorithm, make one shared counter atomic, and give clients a clean 429 contract.
rate-limitingtoken-bucketredis
AdvancedAsked very oftenScalabilitySystem design · Concept
Explain consistent hashing and virtual nodes
Modulo hashing reshuffles nearly every key when the node count changes; a consistent-hash ring with virtual nodes moves only the minimum.
consistent-hashingshardingvirtual-nodes