System Design: Instagram

Design a photo-and-video sharing service with uploads, follows, search, and a feed. Focus on media readiness, visibility rules, and the balance between write-time fanout and read-time assembly.

What is Instagram?

Instagram is a social service for sharing photos and videos. This exercise models a subset: users publish captioned media, follow accounts, and retrieve eligible content through feeds and search. Public discovery and approved-follower access need different visibility rules; hashtags and geotags do not override those rules.

Capacity focus: User growth alone does not determine capacity. Track upload bytes, feed reads, audience size, and the number of derived media versions separately.