Design
Rate Limiter
Design a rate limiter that restricts the number of requests a client can make within a time window.
01 - Why interviewers ask this
It bridges LLD and systems knowledge — interviewers use it to see if you know concrete algorithms (token bucket, sliding window) rather than just saying "we'll rate-limit it" vaguely.
02 - Where this system exists in the real world
You interact with this design every day.
API gateway request throttling
Login attempt / brute-force protection
Third-party API client libraries respecting quotas
03 - What you'll master
Solve this once. Know it forever.
Implement token bucket or sliding window algorithms
Reason about per-client vs. global limits
Understand the single-node version before distributing it
04 - What you'll design
6 functional · 3 non-functional requirements.
Limit requests per user/IP to N per time window (e.g., 100 per minute)
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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