System requirements

Functional:

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

• automated, efficient and user friendly
• dispense a variety of products when correct amount is received
• support multiple payment methods
• product selection
• manage Inventory
• secure transactions

Non-Functional:

List non-functional requirements for the system...

• high availability
• low latency between payment processing and dispensing the product
• security
• performance: should support a large number of simultaneous users efficiently
• reliability: should be reliable and recover from the failures quickly
• scalability: easy to scale to accommodate increased demand
• maintainability: easy to maintain and update
• usability: easy to use for customers

Capacity estimation

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

Users:

• DAU: 500
• Hourly usage: 500 / 8 = 62 users / hour during peak hours

Products:

• 4 categories
• 4 - 6 options per category
• snacks: 20 - 30 units per item
• beverages: 10 - 15 units per item
• Total:
• 4 categories
• 4 * 6 = 24 max options
• 24 * 20 = 480 total quantity of product

API design

Define what APIs are expected from the system...

Inventory management Admin site Flow:

POST api/v1/products

request:

{

products: [

"product_id": id,

"quantity" : int,

"price": float,

"currency": str

]

}

response:

{

status_code: int,

message: str

}

Customer Flow:

step-1: Fetch info about all available products:

GET api/v1/products

response:

{

products: [

"product_id": id,

"quantity" : int,

"price": float,

"currency": str

]

}

step-2: process payment handled by third-party payment gateway

• once the payment is successful, a confirmation along with a payment token is received

step-3: Process payment token from the third party

POST api/v1/payments/process

request:

{

"payment_token": token,

"product_id": id

}

step-4: Dispense the product

POST api/v1/products/{product_id}/dispense

step-5: Update inventory

PUT api/v1/products/{product_id}/update_inventory

request:

{

"product_id": id,

"new_quantity": int

}

response:

{

status_code: int,

message: str

}

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...

Inventory Management:

Products table:

product_id: id (pk)

title: str

ProductsQuantity table:

product_id: id (pk)

quantity: int

ProductPrice table:

product_id: id (pk)

price: float

currency: str

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?