System requirements

Functional:

1. Entry and Exit of Vehicles
2. Payment Service

Non-Functional:

1. Consistent
2. Highly available

Capacity estimation

1. 100 slots for 12 hours are booked
2. 100*24*1Mb = 2400 Mb daily
3. 2400*30*12 = ~ 75 GB yearly

API design

1. POST -> /book-ticket
   1. {vehicle-id, entry-time, vehicle-type}
   2. onboarded
2. POST -> /checkout
   1. {vehicle-id, payment-mode}
   2. payment (success/fail)

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...

High-level design

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?