Instagram — Notes

Functional

• Photo/video upload with filters.
• Feed (home, explore, reels), stories, DMs.
• Like / comment / save.
• Hashtag + user search.
• Notifications.

Non-functional

• 2B MAU, ~100M photos/day, billions of feed opens.
• p99 feed open < 250 ms.

Capacity

• Uploads: 100M/day = 1.2k/s avg, 10k/s peak; avg 3 MB → 3 GB/s peak ingest.
• Storage: 100M × 3 MB × 365 = 110 PB/yr raw; with 3 resolutions and HEVC → ~250 PB/yr.
• Hot CDN: ~1 PB working set.

Schema

• media(id PK, owner_id, type, ts, caption, location, sizes[])
• follow(follower, followee)
• home_feed(user_id, [(ts, media_id)]) Redis ZSET, capped 500.
• stories(id, owner, expires_at)

ID

• 64-bit "Instagram ID": [timestamp ms | shard | seq] Postgres-side generator.

Trade-offs

• Haystack vs S3: Haystack reduces inode metadata overhead for small files.
• Hybrid push/pull for fan-out (same as Twitter).
• Server-side resize vs client adaptive: prefer server-side multiple ladder + CDN.
• AI tagging: improves search/safety but adds GPU cost.

Refs

• Instagram engineering blog (sharding, IDs, feed), Haystack paper, FB TAO paper, ByteByteGo "Design Instagram", Alex Xu Vol 2.