Design An Efficient Parking Lot System - System Design

Requirements

Functional Requirements:

Allow reservation of a parking spot.
Process payment for the reservation.
Enable parking of a car in the reserved spot.
Support early departure before reservation time expires.
Gate check-in/out.
Handle no show.

Non-Functional Requirements:

Reliability
High Availability
Secure
Strong Consistency

API Design

RESERVE PLACE

POST /reserve
  {
    "car_plate": "str",
    "lot_id": "str",
    "check_in_time": "timestamp",
    "check_out_time": "timestamp"
  }
RESPONSE
{
"reserve_id": "str",
"price": "str"
}

CheckIn

REQUEST

POST /lot/check-in
{
"car_plate": "str
}

RESPONSE

SUCCESS

NO ACTUAL RESERVATION FOR THIS VEHICLE FOUND

CheckOut

POST /lot/check-out
{
"cat_plate": "str
}

RESPONSE

SUCCESS

THERE IS A PARKING DEBT FOR A VEHICLE

List of parking lots

GET /parking
{
lot_ids: ["str", "str", ...]
}

GET /parking?free=ture&size=medium
{
lot_ids: ["str", "str", ...]
}

GET /parking/{id}
{
lot_id: "str"
}

POST /parking/debt
{
"car_plate": int
}

POST /parking/pay

REQUEST

{
"car_data": "str"
"car_plate": "str"
}

High-Level Design

There should be 3 types of business entities: parking lots, reservations and actions.
Data should be consistent, everything can be stored in simple RDBMS.
User visits FrontEnd, FrontEnd asks car size and car plate, after user typed it in, FrontEnd makes request for available parking lot of requested size. User click on lot which is good for him, that sends reservation request to BackEnd. After that user have link to payment processing. If payment is processed everything is ok. Camera makes a photo of every plate and autmatically tries check-in/check-out request
LoadBalancer is used in case of traffic burst
Ingress limits amount of RPS for IP, so users won't overload system by f5 on available place.

Detailed Component Design

RDBMS structure:
- Parking lot has: ID, Size (Small, Medium, Big), Price
- Reservation has: ID, car_plate, TSTZRANGE, payed, create_time, expired
- Action has datetime, action [check_in, check_out]
When user create reservation it considers as non free for 15 minutes. 15 minutes after create_time it becomes free if not payed. Free/Non Free logic is Bussiness logic, not something that is saved in db but determined on request
GiST extension of postgres will provide strong consistency, so reservations won't overlap
check-in works only if there is payed reservation found in correct timescope for the car_plate
Parking debt exist in case if there is created parking which is not payed or in case checkout hasn't happened and there is 5 minute after checkout time
If parking debt > 0 checkout won't happen
If someone created reservation it is not considered "Free", so it cannot be reserved. The one who first reserved it got it. After reservation made websocket sends to Client information that place is not available anymore.
Every minutes cron job check whether there are new places available, if yes then websocket sends message to Client about new lot
If payment is successfull then reservation payment is set to true, otherwise set to false, BackEnd send Client message so client should retry payment.
All Payment are delegated to PaymentProcessor. PaymentProcessor just validates data a send it to some credit card payment processor (Bank or Merchant)
System won't allow to make overlapping interval.

Requirements

Functional Requirements:

Allow reservation of a parking spot.
Process payment for the reservation.
Enable parking of a car in the reserved spot.
Support early departure before reservation time expires.
Gate check-in/out.
Handle no show.

Non-Functional Requirements:

Reliability
High Availability
Secure
Strong Consistency

API Design

RESERVE PLACE

POST /reserve
  {
    "car_plate": "str",
    "lot_id": "str",
    "check_in_time": "timestamp",
    "check_out_time": "timestamp"
  }
RESPONSE
{
"reserve_id": "str",
"price": "str"
}

CheckIn

REQUEST

POST /lot/check-in
{
"car_plate": "str
}

RESPONSE

SUCCESS

NO ACTUAL RESERVATION FOR THIS VEHICLE FOUND

CheckOut

POST /lot/check-out
{
"cat_plate": "str
}

RESPONSE

SUCCESS

THERE IS A PARKING DEBT FOR A VEHICLE

List of parking lots

GET /parking
{
lot_ids: ["str", "str", ...]
}

GET /parking?free=ture&size=medium
{
lot_ids: ["str", "str", ...]
}

GET /parking/{id}
{
lot_id: "str"
}

POST /parking/debt
{
"car_plate": int
}

POST /parking/pay

REQUEST

{
"car_data": "str"
"car_plate": "str"
}

High-Level Design

There should be 3 types of business entities: parking lots, reservations and actions.
Data should be consistent, everything can be stored in simple RDBMS.
User visits FrontEnd, FrontEnd asks car size and car plate, after user typed it in, FrontEnd makes request for available parking lot of requested size. User click on lot which is good for him, that sends reservation request to BackEnd. After that user have link to payment processing. If payment is processed everything is ok. Camera makes a photo of every plate and autmatically tries check-in/check-out request
LoadBalancer is used in case of traffic burst
Ingress limits amount of RPS for IP, so users won't overload system by f5 on available place.

Detailed Component Design

RDBMS structure:
- Parking lot has: ID, Size (Small, Medium, Big), Price
- Reservation has: ID, car_plate, TSTZRANGE, payed, create_time, expired
- Action has datetime, action [check_in, check_out]
When user create reservation it considers as non free for 15 minutes. 15 minutes after create_time it becomes free if not payed. Free/Non Free logic is Bussiness logic, not something that is saved in db but determined on request
GiST extension of postgres will provide strong consistency, so reservations won't overlap
check-in works only if there is payed reservation found in correct timescope for the car_plate
Parking debt exist in case if there is created parking which is not payed or in case checkout hasn't happened and there is 5 minute after checkout time
If parking debt > 0 checkout won't happen
If someone created reservation it is not considered "Free", so it cannot be reserved. The one who first reserved it got it. After reservation made websocket sends to Client information that place is not available anymore.
Every minutes cron job check whether there are new places available, if yes then websocket sends message to Client about new lot
If payment is successfull then reservation payment is set to true, otherwise set to false, BackEnd send Client message so client should retry payment.
All Payment are delegated to PaymentProcessor. PaymentProcessor just validates data a send it to some credit card payment processor (Bank or Merchant)
System won't allow to make overlapping interval.