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List functional requirements for the system (Ask interviewer if stuck)...
able to post tweets
follow other users
get the feed of followed users
search tweets
List non-functional requirements for the system...
highly available,
scalable
Estimate the scale of the system you are going to design...
1 billon tweets per day
10k per seconds
peak time 50k per seconds
storage 100 Gb per day
Define what APIs are expected from the system...
api/v1/send: post, send a tweet
api/v1/read: get, read the followed tweets
api/v1/search post, search a tweet
api/v1/follow: post, follow a user
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...
account:
user_id:
user_name:
relationship:
follower_id:
following_id:
tweet db:
post_id:
post_content
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...
B[client] --> C{server}
C --> D[content]
C --> E[search]
C --> F[Follower/following]
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...
Read:
flowchart TD
B[client] --> C{server}
C -->|read following| E(relationship db)
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...
Explain any trade offs you have made and why you made certain tech choices...
Try to discuss as many failure scenarios/bottlenecks as possible.
What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?