System requirements

Functional:

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

This is essential for ensuring only registered users can publish advertisements.

Users can search for advertisements by keywords and view the found advertisements.

The users can edit their advertisements.

The user can delete their advertisements

The admin can add the sections to structure the advertisements.

Non-Functional:

List non-functional requirements for the system...

This service should be highly available.

This service should be highly scalable.

When users publish new advertisements, they appear within 10 milliseconds.

The service should be highly reliable.

Only registered users can publish, edit, and delete the advertisements; others may only read.

The advertisements will be shown in chronological order in the board messages.

The advertisements can have only text.

Capacity estimation

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

The section of advertisement information:

id long (8 bytes)

parent_id long (8 bytes)

name string (200 bytes)

description string (1024 bytes)

createdAt timestamp (4 bytes)

changedAt timestamp (4 bytes)

The advertisement information:

id long (8 bytes)

parent_id (8 bytes)

content string (2048 bytes)

changedAt timestamp (4 bytes)

createdAt timestamp (4 bytes)

user_id long (8 bytes)

The user information:

id long (8 bytes)

email string (200 bytes)

nickname string (100 bytes)

createdAt timestamp (4 bytes)

role string(1 byte)

status string (1 byte)

Let's have 1 MAU. Every user can read the advertisement 5 times daily and publish a new advertisement 2 times a week.

Every advertisement takes 2 kilobytes, and it takes 4 gigabytes per year to store added advertisements, or 40 Gigabytes for 5 years.

In order to search the advertisement we introduce the reverse index.

The reversed index contains a word and a list of unique IDs, where each unique ID takes 8 bytes. Let's count the every word take 100 unique ids and it has 1 million words and every word takes 500 bytes. In total, it takes 8 PetaBytes.

API design

Define what APIs are expected from the system...

The Craigslist can benefit from a well-defined set of API to facilitate communication between different component and potentially integrate with external systems. Here's a breakdown of potential APIis:

User API:

• GET /catalog/search?words=word1,word2: retrieves a list of the advertisements that contain the given words
• GET /catalog/{id} retrieves the advertisements by id
• PUT /catalog/{id} edits the advertisement
• PUT /catalog publishes new advertisement
• DELETE /catalog/{id} deletes the advertisement

Admin API:

• GET /section/{id} retrieves the section description by id. It may contain all the underlying sections and advertisements
• GET /section/all?page=1 retrieves the list section by using paging.
• PUT /section/{id} updates the section
• POST /section adds a new section to the section structures.
• DELETE /section/{id} removes the section.

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...

We use PostgreSQL, which we favor for strong consistency over availability.PostgreSQL is scalable and fault-tolerant.

The section of advertisement information:

id long (8 bytes)

parent_id long (8 bytes)

name string (200 bytes)

description string (1024 bytes)

createdAt timestamp (4 bytes)

changedAt timestamp (4 bytes)

The advertisement information:

id long (8 bytes)

parent_id (8 bytes)

content string (2048 bytes)

changedAt timestamp (4 bytes)

createdAt timestamp (4 bytes)

user_id long (8 bytes)

The user information:

id long (8 bytes)

email string (200 bytes)

nickname string (100 bytes)

createdAt timestamp (4 bytes)

role string(1 byte)

status string (1 byte)

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...

We will take microservice approach. Advertisement service manages the ads API. If ads is updated, Advertisement service sends an update event to Search service to update index.

Request flows

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?