Design a reservation and payment system for a parking garage

I’m up to 4m01s

Clarifying questions I came up with

<what do I call this category?> Who are the users for this system? Is it web only, or mobile app?
- Does the reservation system need to have the same front end as the payment system? or can they be separate, e.g. reservation is a mobile app, but payment is backend only
Scale: How many users does this system need to handle today?
- Do we anticipate any growth in the next year or two?
Security: Are there any specific security / authentication requirements we need to take into consideration?
- What user data are we collecting - I assume the bare minimum.
Integrations: Does this system need to integrate with any other systems?
- Payments in particular - will we be integrating with a 3rd vendor who will handle all the PII for us?

Then prompted by YouTube:

Product specs:
- Reservation: user needs to be able to view available spots, pick one, pay for it and get a receipt
  - How far in advance can we book? Do we need to support same day reservations?
    - If so, then how do we know which spots are available? Automatic sensors?
- Types of parking spot: e.g. handicapped, size of vehicle, long stay vs short stay
- Availability of spots: how does the system know? Can I assume there are sensors on the ground?
- Prices for the garage: flat rate, different for each size of vehicle
- Payment methods:
  - cash only via physical terminal? Credit card supported? Barcode scanning from shopping centre?
  - Can I pay on exit, or is it upfront payment only?
- Login required?
- Do we need to support rescheduling after payment?
  - e.g. want to change the date, or change the vehicle type
  - Do we need to support refunds? e.g. if they go from large to small
Backend “consistency”: need to make sure two users can’t reserve the same spot
- I would have called this reliability

User Interface (web app / mobile app)

→ Load balancer (probably not required for a small garage

→ Web server

Login (if needed)
GetSpots
- From cache
SelectSpot / ReserveSpot POST
- Mark the spot as unavailble for X minutes
- Select vehicle type
- select duration
PaymentService
- Select method
- Integration with 3rd party payment provider
Confirmation
- Update DB and cache
Clean up (if user backs out of flow)
- Mark the spot as availble again

Public endpoints

GET /availableSpots?date=2025-02-22
- Assumption: simple system - a user does not get to choose the spot, just reserves one if it exists
  - more complex system - a user can see all the spots, available and taken, and choose the exact spot they want
- Returns 200 with a body, that can be parsed by the UI into a visual schematic for the user. Most likely some kind of grid
This GetAvailableSpotsService
- Retrieve information from a cache or DB about which spots are available for that given day
- Is this a cache or a DB? Depends on the speed we need it.
- Probably DB is fine
  - Relational or non-relational?
  - Relational if we want a more complex system, e.g. we want to know WHO has booked which spot on a given day
  - Non-relational if all we need is a simple view of the available spots
  - So perhaps we end up with a mix of the two.
  - Non relational to quickly populate the GET
  - Then as part of the PaymentService, we will
    - Write to the DB
    - Update the cache
- We can talk about the DB / table structure if we want to. For now, let’s just move on

QUESTIONS / further research

System design: design a parking garage, WIP