Requirements

Functional Requirements:

• Allow users to tweet messages up to 140 characters.
• Enable users to follow other users.
• Allow users to like tweets from other users.
• Display tweets from followed users in the home feed.
• Show top K popular tweets in the home feed based on likes and followers.

Non-Functional Requirements:

• Eventual consistency on feed
• Strong consitency on stored messages / likes
• At least 90% SLA
• Low latency on the user feed (loading a feed should be ms rather than seconds)

API Design

External service - Users

UserFeedEntry - Generated feed for the user

Tweet - Message created by the user

TweetLikes - Storage for likes

Follow - Entity representing a follow from user a to user b

Routes:

/users/{id}/feed - get current feed of the user

/users/{id}/tweets - post new tweet

/tweets - api for tweets - access etc.

High-Level Design

Tweets are being stored as a single entry, with user relation etc.

Tweet likes are stored separately so we have possibility to access who left a like instead of having a simple counter

Follows are used to create UserFeedEntry

We store these entries each time a followed person leaves a new post

Then when accessing the data, we can sort it and limit how we want. With proper indexes it should be quick.

Detailed Component Design

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.