These are HLD questions of the kind Meta actually asks — the patterns reported from Meta's AI-engineering rounds, where design trade-offs, scale and failure modes matter as much as definitions. Treat this page as a mock interview: say every answer out loud before revealing it. If one surprises you, the lesson behind it is linked at the bottom.
Meta HLD concept questions
Meta interviewers frequently ask about designing a news feed. What is the core trade-off between 'fan-out on write' (push a new post to all followers' feeds immediately) and 'fan-out on read' (compute the feed when a user opens the app)?
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A Meta interviewer asks why it's acceptable for a 'like' count to be slightly wrong for a few seconds after a user likes a post, but not for the post's actual content to ever be shown incorrectly to the wrong audience (e.g. a private post visible to strangers).
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Meta HLD applied & hands-on questions
Meta-style: your news feed uses fan-out on write. A celebrity account with 100 million followers posts. Design how your system avoids triggering 100 million immediate writes.
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How to use this page: Meta rarely asks something you've never seen — they ask a standard HLD concept and then push one level deeper ("why?", "what would you do if..."). Master the concept in the HLD course lessons, and the follow-up stops being scary.
Keep practising: Caching Explained, Databases at Scale, Design a URL Shortener and Interview Framework cover what most Meta HLD rounds test.