Design Instagram / Image Feed

System DesignRobloxLast reported June 2026Medium Frequency
Reported
5× across candidate reports
First seen
February 2025
Last reported
June 2026
Reported outcome
mixed

Problem Overview

Two major variants observed under the same title: (1) Backend System Design (Instagram): Design Instagram with emphasis on the post feed — specifically how to display personalized social engagement ('Tom, James liked this post') and aggregate like counts ('500k people liked this post'). Key challenge: handling the hot key /…

  • 4 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
  • The rest of the problem statement — full requirements, constraints, and edge cases
  • Approach and trade-offs — what passing candidates did, and the mistakes that sink people
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Verified Source
Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.
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