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LLDsystem_design~12 mins

Why parking lot is a classic LLD problem - Architecture Impact

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System Overview - Why parking lot is a classic LLD problem

A parking lot system manages vehicle parking efficiently. It handles vehicle entry, slot allocation, payment, and exit. The system must support different vehicle types and optimize space usage.

Architecture Diagram
User
  |
  v
Entry Gate -> Ticket Dispenser -> Parking Slots -> Payment Booth -> Exit Gate
  |             |                  |               |             |
  +-------------+------------------+---------------+-------------+
                                Parking Lot Management System
                                         |
                                         v
                                   Database
                                         |
                                         v
                                       Cache
Components
User
actor
Person driving vehicle to park or exit
Entry Gate
service
Controls vehicle entry and triggers ticket issuance
Ticket Dispenser
service
Generates parking ticket with slot info
Parking Slots
resource
Physical parking spaces for vehicles
Payment Booth
service
Handles payment processing before exit
Exit Gate
service
Controls vehicle exit after payment verification
Parking Lot Management System
service
Coordinates slot allocation, ticketing, and payments
Database
database
Stores vehicle, slot, ticket, and payment data
Cache
cache
Speeds up frequent slot availability checks
Request Flow - 14 Hops
User → Entry Gate
Entry Gate → Parking Lot Management System
Parking Lot Management System → Cache
Cache → Parking Lot Management System
Parking Lot Management System → Database
Parking Lot Management System → Ticket Dispenser
Ticket Dispenser → Entry Gate
User → Parking Slots
User → Payment Booth
Payment Booth → Parking Lot Management System
User → Exit Gate
Exit Gate → Parking Lot Management System
Parking Lot Management System → Database
Exit Gate → User
Failure Scenario
Component Fails:Database
Impact:New slot allocations and payment updates fail; system cannot persist state changes
Mitigation:Use cache for read operations to allow slot availability checks; queue write operations for retry; implement database replication for high availability
Architecture Quiz - 3 Questions
Test your understanding
Which component is responsible for assigning parking slots to vehicles?
ATicket Dispenser
BParking Lot Management System
CPayment Booth
DExit Gate
Design Principle
This parking lot system demonstrates key low-level design principles: modular components with clear responsibilities, use of caching to improve performance, and a reliable flow for resource allocation and payment processing. It models real-world constraints like slot availability and payment verification, making it a classic example for learning system design.