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:

• List the key non-functional requirements (eg low latency, scalability, reliability, etc.)...
• Scalability would be the first thought on this problem there could be peak hours where many users are online at the same time so we would want load balancer to help scale the requests to the servers

API Design

Define the APIs expected from the system. This is your chance to analyze and define the read and write paths so that you can come up with the high-level design...

There are a few major functions in this app

• Following friends
• Posting tweets
• Liking tweets
• Seeing popular tweets and your friends' tweets on your feed
  • We need some sort of algorithm to calculate the popular tweets
  • We need some sort of algorithm to rank your friends' tweets
    • Both these algorithms should take into account the recency of the tweet and the number of likes it has received

We can summarize these as the following:

• Taking actions on the site to interact (i.e., liking a post, tweeting, following users)
• Getting an updated feed

Models

• Table for users
  • ids, emails, relation to followers, relation to followed by users
• Table for tweets
  • id, content, user_posted, likes, created at
• Table for likes
  • id, tweet id, user id, created at

High-Level Design

Describe the overall system architecture. Identify the main components needed to solve the problem end-to-end. Use the diagramming tool to create a block diagram.

• Client sends a request to webserver
• A load balancer processes requests to ensure distribution
• The server processes the request once it is authenticated and rate-limited (we may have bad actors trying to take down our system by sending too many tweets, too many follows, etc).
• Posting a tweet service, liking a tweet service, follow user service
  • These services should also trigger a fan-out service which will asynchronously update user feeds
  • This can be a pub/sub relationship since we don't want to update user feeds until we refresh

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.

The fanout service uses a message queue to publish and subscribe to any changes that would impact the user's feed. We don't need real-time responses, so we send the request to a message queue to fan out workers to work on updating the feed cache. The fanout service should also check the user DB to update the user's followers' feeds.

The feed service will need to search for the latest tweets with the highest likes, maybe we can do a search timeboxed to tweets posted today and sort them by likes and then the time posted