System requirements

Functional:

Create tweet

Update tweet

Delete tweet

Follow / Un-follow user

Retweet

Get list of recent tweets

Be able to directly message another user

Create an account

Non-Functional:

Should be highly available with minimal latency

Get list of recent tweets should be displayed quickly when accessing the website

Extended requirements:

Have some metrics + Like posts

Should receive some notification of new tweet available

Capacity estimation

Number of daily users 2M

Ratio read / write : 100 / 1

Request in READ per day 200M, per second 200M / 24 * 3600 = 86 400 per sec

Request in WRITE per day 2M, per second 2M / 24 * 3600 = 864 requests per sec

Storage required:

One tweet / 100 will contain media such as image / video. Average of 1MB. So per day with need 20GB of bandwidth +

99 tweets / 100 will contain maximum 240 characters. Around 1KB of data so 1.98M request * 1KB = 1 980MB = 1.9GB of bandwidth in total

API design

createTweet(userId: string, tweet: char[]): TweetId

updateTweet(userId: string, tweet: char[]): TweetId

deleteweet(userId: string, tweetId: string): TweetId

followUser(userId: string): boolean with true if follow is a success

unFollowUser(userId: string): boolean with true if unfollow is a success

retweet(tweetId): TweetId of new tweet

like(tweetId): boolean with true if follow is a success

getRecentTweets(userId: string): Tweets[]

message(userId: string): boolean with true if follow is a success

createAccount(userPseudo:string, password:string)

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...

tweet

id : string primary key

userId: string foreign key

content: string

likeCount: int

createdAt: string

user

id : string primary key

email:string

username : string

password: string

following

followedId: string foreign key on user id

followerId: string foreign key on user id

timestamp:string

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...

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?