System Design — Instagram

Product Requirements

1. [Post] User can create a post (image + text (optional))
2. [Post] User can comment on a post
3. [Post] User can like a post
4. [Feed] User can get follow feed ordered by time (landing page)
5. [Feed] User can get profile feed of another user ordered by time

The above functionalities can be grouped into two: post and feed.

Follow feed is the default landing point, thus has to handle heavy traffic. It’s worth to put much engineer effort to it.

Non-product Requirements

1. Performance: low latency, follow feed should be fast cause it’s the landing point
2. Persistency: contents uploaded by user must not be lost
3. Accuracy: order of post and number of likes user receives can be less strict.

Interface/API

1. create_post(user_id, image, text, timestamp) -> success/failure

• assume every post has an image, and optional text

2. comment_post(user_id, post_id, comment, timestamp) -> success/failure

• assume you can comment on a post, but not on another comment