System requirements

Functional:

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

1. post comments
2. view comments
3. post comments on to a video
4. view comments on the video by others

Non-Functional:

List non-functional requirements for the system...

1. Multiple users should be able to post comments at the same time onto a video
2. scale for millions of users
3. system should be reliable
4. system should be accurate
5. low latency in reflecting the comments. should be real time.

Capacity estimation

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

1. One comment can be of size 500MB
2. No of comments per user per video can be set to 10.
3. system is read heavy.

API design

Define what APIs are expected from the system...

1.Create a comment

POST - / v1/user_id/video_id

{

comment: {comment}

}

{

comment_id

}

2.Edit a comment

PATCH - /v1/user_id/video_id/{comment_id}

{

comment

}

{

}

DELETE

v1/user_id/video_id/comment_id

{

comment_id

}

{

OK

}

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...

Store all the comments of a single video in one shard

Video table

video_id

user_id (user uploaded the video)

creation_time

video table is sharded on user_id

Comments table

video_id

comment_id

comment_user_id:

Comments table is sharded on video_id

Indexed on comment_user_id

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...

1. User comments on a video
2. server pushes the message to the kafka
3. message payload contains :

{

video_id

user_id

comment_id

}

kafka partitioned on video_id

all the comments of a video go into single partition

consumer picks up message and give it to gateway

gateway checks this user_id and video_id are connected to which webserver and sends the message there. webserver is connected to clients via persistent connnection.

1. client opens a connection with a server.
2. client registers with the web servers , web server stores the mapping into redis.
3. gateway server looks into mapping from redis and calls respective webserver.
4. webserver pushes the comment to the client watching the video.

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?