System requirements
Functional:
Write Post
Post Post
Share Tweets
Follow Users
View news feed
Like and react to posts
Follow and unfollow users
Account Authentication
Non-Functional:
Eventual Consistency on News Feed
Low Latency
Highly availability
Highly reliable
Fault tolerance
Capacity estimation
Let's assume 300,000,000 MAU
Unique DAU 10,000,000
Peak concurrent users: 1,000,000
QPS: 1,500,000
This would be a Read heavy system. Let's assume 20% of QPS are Writes: posts, likes, comments and the other 80% are Reads
For the actual storage:
300,000 QPS at something like 0.5KB
150,000 KB = 150MB * 60 = 9000 MB per minute = 9GB per minute 540 GB per hour
500GB *24 = 12,000 = 12 TB per day
3.6 PB per year
API design
Define what APIs are expected from the system...
post Posts (authentication_tokern, message)
get Posts (authentication_token, user_id, hashtag_id, search_params_
patch Posts (authentication_tokern, message)
post Like
post comments
get Like
get Comments
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...
user table
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...
Mobile Front End
Load Balancer/Api Gateway
CDN (for popular posts)
Sharded database
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...
The CDN would have both push and pull mechanisms.
Trade offs/Tech choices
Explain any trade offs you have made and why you made certain tech choices...
I would use primarily NoSQL. the actual tweets, posts, comments, and replies could be stored in a NoSQL document type storage. I was additionally use Blob storage for the photos and videos that users upload.
-Focus on high availability
-quick write times
-highly reliable, can have a lot of replication
SQL is not as good a choice since the write time may be significant, but SQL can be used for overall user meta data that doesn't change as much and is more relational
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?