System requirements

Functional:

• should be able to see a collection of posts from the profiles and pages they follow.
• Posts should be ranked based on relevance, timelines and user interaction.
• User should be able to engage with likes, comments and shares
• Real time updates
• User should receive notifications

Non-Functional:

• Availability > consistency
• Highly available
• Low latency
• Real-time updates
• DAU - 1.2 billion

Capacity estimation

DAU - 1.2 billion

Avg time per user - 20 mins per day

avg time on posts - 5 sec

Total posts = 1200/5 = 240.

Reads ~ 57k reads per sec.

10% are active users and add 2 posts per day

120000000*2 = 2.4million posts per day =

writes ~2500 posts per sec.

API design

GET /v1/posts?Pagination={}&sort=+{time} -> Partial

GET /v1/posts/:id -> Post

POST /v1/posts/:id/comment

POST /v1/posts/:id/like

Core Entities

Post

• postId
• authorid
• content
  • metadata
  • location
• timestamp
• numberOfLikes
• List<Comments>
  • commentId
  • authorId
  • content<TEXT>
  • timestamp
  • List<comments>

User

• userId
• profile
• following<User/Page>
• followers<user/Page>
• List<Posts>

Page

• PageId
• following<User/Page>
• followers<user/Page>
• List<Posts>

High-level design

In this diagram:

• The Client (browser or app) sends requests to the CDN.
• The CDN queries the Reverse Proxy, which then directs requests to both the ReadNewsFeedService and WriteNewsFeedService depending on the nature of the request.
• The ReadNewsFeedService retrieves data from the Read Cache for faster access.
• The WriteNewsFeedService writes content to the Write DB for storage.
• We have a Change Data Capture (CDC) process that updates the cache whenever there is a write operation to the Write DB.
• The NotificationService receives updates via the cache and sends notifications back to the Client.

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?