System requirements

Functional:

List functional requirements for the system (Ask the chat bot for hints if stuck.)...

1. User can resgister, login, change profile, follow/unfollow
2. User can post photos, delete photos
3. User can get personalized feed based on users followed
4. User can send a message to another user
5. User can comment/like on a post.
6. User can receive notifications (new feed, new followers, new messages)

Non-Functional:

List non-functional requirements for the system...

1. Low latency: upload < 1s, download < 200ms,
2. Highly available > 99.9%, downtime at most 4 hours anually.
3. Scalability with 20% growth anually.
4. Maintainability, should be easy to troubleshoot.

Capacity estimation

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

1. Total users: 100m
2. Daily active users: 40m, 80m at peak
3. User metadata (profile pic, username, followers, comments): 10kb per user, total = 10kb * 100m = 1TB
4. Photo storage: 1mb per image, 100kb per thumbnail.

on average, each user posts 10 photos, total photo storage = (1.1mb) * 10 * 100m, round down to 1 PT

1. 1. Backup photo storage: 2PT
   2. Total = 1PT + 2PT = 3PT

API design

Define what APIs are expected from the system...

POST /v1/register

GET /v1/login

POST /v1/post

POST /v1/uploadPhoto/{:filePath}

POST /v1/deletePhoto/{:id}

GET /v1/getFeed/{:id}

POST /v1/sendMessage

POST /v1/comment/{:id}

POST /v1/like/{:id}

GET /v1/pushNotification/{:id}

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...

UserDetails

-user_id: UUID (PK)

-username: string

-hashed_password, string

-bio: string

-created_at: datetime

-is_active: boolean

-last_login: datetime

-profile_pic: string, URL

-following_counts: int

-followers_counts: int

Comments:

-comment_id: int

-comment: string

-user_id: foreign key referencing UserDetails

Photos:

-photo_id: int

-photo_url: URL in S3

-thumbnial_url: URL in S3

-upload_date: datetime

Message:

-message_id: int

-content: string

-sent_date: string

-sent_to: user_id foreign key referencing UserDetails

Feed:

-feed_id: int

-user_id: user_id foreign key referencing UserDetails

-post_id: foreign key referencing Posts

-added_at: datetime

-seen: boolean, weather the user has seen the feed

Posts:

-post_id: int

-photo_id: foreign key referencing Photos

-user_id: foreign key referencing UserDetails

-photo_url: URL to the photo in S3

-like_count: int

-is_private: boolean

-caption: string

-post_date: datetime

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?