System requirements

Functional:

• post with images and text
• follow users
• see post feed
• create comments and likes

Non-Functional:

• scalable
• load post feed quickly

Capacity estimation

Estimate the scale of the system you are going to design...

100M users

1 post/day per user

100KB/post

365 * 100KB * 100M = 10 TB/year

API design

• create post
• follow user
• show feed
• create comments
• like post

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

SQL database

• user database (user_id, name, ...)
• post database (post_id, user_id, text, img_url, ...)
• comments (comment_id, post_id, text)

store img in s3

store popular posts in CDN

to find posts in a feed for a user. Find posts created by followed users

High-level design

You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...

Client send request to see post feed

• goes into load balancer to evenly distribute requests to multiple servers
• Server find posts in database that the user follows
• retrieve img from S3

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?