Art of Codeartofcode
Lesson 4 of 15

37. Design a News Feed

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The interview prompt
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37.1 What do you ask first?
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37.2 How big is this, really?
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37.3 What are the doors?
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37.4 What do we store?
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37.5 What does the whole system look like?
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37.6 Fan-out on write or on read?
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37.7 How do you solve the celebrity problem?
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37.8 How does ranking work?
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37.9 How do the feed cache and pagination work?
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37.10 What would you say in the last five minutes?
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Score yourself
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Variations to practise
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Sources
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Code lab
37. Design a News Feed

37.3 What are the doors?

3 min read+10 XP

Step 3: API and data model (10 minutes)

POST /v1/posts { "text": "...", "media_ids": ["m_91"] } → 201 { "post_id": "p_123" } POST /v1/users/{id}/follow → 204 GET /v1/feed?cursor=...&limit=20 returns: { "items": [ { "post_id": "p_123", "author": {...}, "text": "...", "media": [...], "likes": 41, "created_at": "..." }, ... ], "next_cursor": "c_8f2..." , "new_posts_available": 3 }

Media is uploaded separately to object storage with presigned URLs (Chapter 11) and served through a CDN (Chapter 26); posts only reference media IDs.