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A parking lot system must handle:
Beyond basic functionality, the system should also ensure:
To simplify, let’s assume:
### **Parking Lot System API Design**
This design separates concerns into three main services: **Entry**, **Exit/Payment**, and **Account/Admin**.
#### **1. Entry Gate Service**
Handles vehicle arrivals, slot allocation, and ticket issuance.
* **`POST /api/v1/parking/entry`**
* **Description:** Triggered when a vehicle reaches the entry gate. Allocates a spot and issues a ticket.
* **Request Body:**
```json
{
"entry_gate_id": "GATE_01",
"vehicle_number": "ABC-1234",
"vehicle_type": "CAR" // Enum: CAR, MOTORCYCLE, TRUCK, EV
}
```
* **Response (200 OK):**
```json
{
"ticket_id": "TKT_998877",
"vehicle_number": "ABC-1234",
"slot_id": "L1_R3_S10",
"entry_time": "2025-10-27T10:00:00Z",
"bar_code": "binary_data_or_url"
}
```
* **Error (409 Conflict):** `{"message": "Parking Lot Full"}`
#### **2. Exit & Payment Service**
Handles ticket validation, fee calculation, and transaction processing.
* **`POST /api/v1/parking/fee`**
* **Description:** Triggered when a user scans their ticket at the exit or payment kiosk to see the amount due.
* **Request Body:**
```json
{
"ticket_id": "TKT_998877",
"exit_time": "2025-10-27T12:00:00Z" // Optional, defaults to now
}
```
* **Response (200 OK):**
```json
{
"ticket_id": "TKT_998877",
"duration_hours": 2.0,
"amount_due": 15.00,
"currency": "USD",
"status": "UNPAID"
}
```
* **`POST /api/v1/parking/payment`**
* **Description:** Processes the payment for a specific ticket.
* **Request Body:**
```json
{
"ticket_id": "TKT_998877",
"amount": 15.00,
"payment_method": "CREDIT_CARD", // CASH, APPLE_PAY
"payment_reference": "TXN_554433"
}
```
* **Response (200 OK):**
```json
{
"payment_id": "PAY_001",
"status": "SUCCESS",
"receipt_url": "https://api.parking.com/receipts/PAY_001"
}
```
* **`POST /api/v1/parking/exit`**
* **Description:** Final validation at the exit gate barrier. Checks if the ticket is paid/valid before opening the barrier.
* **Request Body:**
```json
{
"ticket_id": "TKT_998877",
"exit_gate_id": "EXIT_02"
}
```
* **Response (200 OK):**
```json
{
"authorized": true,
"gate_action": "OPEN",
"message": "Have a nice day"
}
```
#### **3. Slot & Monitoring Service (Admin/Dashboard)**
Used by internal systems and operator dashboards.
* **`GET /api/v1/slots/availability`**
* **Description:** Returns the count of available spots per type/level.
* **Response:**
```json
{
"total_capacity": 500,
"available_count": 42,
"breakdown": {
"CAR": 30,
"MOTORCYCLE": 10,
"EV": 2
}
}
```
---
In interviews, highlighting slot categorization, allocation algorithms, and real-time updates shows you can think beyond the basics of designing a parking lot System Design and optimize for usability.
Smooth entry and exit flows are essential to prevent congestion. When figuring out how to design a parking lot System Design, this flow integrates physical infrastructure with backend logic.
Tickets are the backbone of accountability in how to design a parking lot System Design. They link a vehicle to a slot, a time, and ultimately, a payment.
In interviews, focusing on ticket lifecycle and fraud prevention demonstrates awareness of real-world issues in your answer for “design a parking lot System Design”, which goes beyond just “assigning slots.”
A parking lot isn’t just about allocating spaces—it’s also about revenue collection. When figuring out how to design a parking lot System Design, the payment system ensures accurate fee calculation, secure transactions, and a smooth user experience.
Behind every smooth entry, slot allocation, or payment is a well-structured database. When answering how to design a parking lot System Design, the schema must capture entities, relationships, and ensure real-time accuracy.
One of the biggest challenges in problems like design a parking lot System Design is handling concurrency. Multiple cars may enter or exit at the same time, and the system must ensure slot allocation and payments remain consistent.
A real parking lot system cannot afford to go down during rush hour. If gates stop working, payments fail, or tickets can’t be validated, it leads to chaos and lost revenue. That’s why fault tolerance is a cornerstone of your answer to “design a parking lot System Design”.
What works for a 50-car lot doesn’t necessarily work for a multi-level airport parking garage or a chain of lots across a city. Scalability ensures the system can grow without breaking.