# Design a car rental platform: system design interview question

> Vehicle reservations across time intervals, with preparation time, hold deadlines, late returns, and durable confirmations.

Source: https://sysround.com/questions/design-car-rental-platform
Updated: 2026-11-05


Difficulty: hard. Levels: Senior, Staff+.

## How the interviewer opens it

"Design a car rental platform. Customers search across rental locations and reserve vehicles for a pickup and return time."

## What to clarify first

- Fleet and locations
- Traffic and read-to-write ratio
- Vehicle selection
- Rental duration and locations
- Hold deadline
- Vehicle operations and readiness
- Latency
- Consistency and availability
- Durability and history
- Scope limits

## Scope of a strong answer

Core requirements:

- Search for available vehicles by location, vehicle class, and rental interval.
- Hold and confirm a reservation without conflicting reservations.
- Cancel a reservation and release its vehicle.
- Account for preparation, maintenance, pickup, and actual return.

Usually out of scope:

- Payments, insurance, and dynamic prices.
- One-way rentals and vehicle transfers.
- Vehicle telemetry and repair work.

## What interviewers probe

### Reservation conflicts and durability

One vehicle can support many future reservations. Concurrent requests and database failures must not create overlapping commitments or erase acknowledged confirmations.

### Hold deadlines

Expiry, delayed requests, and retries can race. The service needs one acceptance boundary and one durable result.

### Vehicles that are not ready

A valid schedule does not prove physical readiness. Delays and safety faults can affect both new requests and existing commitments.

### What an available search result means

Search must remain fast and at most 30 seconds stale. Even a fresh result cannot promise that a later hold will succeed.

## Common mistakes

- The design checks only pickup time and ignores the full rental interval plus preparation.
- The design treats search as a reservation or ignores the age of its source data.
- The design protects existing reservations but leaves a vehicle with no reservations open to a race.
- The design uses different expiry rules for confirmation and release.
- The design acknowledges confirmations that one database node failure can erase.
- The design flags delays or faults but still accepts new holds for unavailable vehicles.

## The bar by level

- **Senior:** The candidate defines atomic changes across holds, confirmation, expiry, and staff events. They handle duplicate commands, uncertain outcomes, and bounded search freshness. They preserve acknowledged confirmations.
- **Staff+:** The candidate proves safety across failover and partitions. They order delayed vehicle events correctly. They quantify query cost and contention. They define recovery when physical capacity cannot meet confirmed commitments.

Practice this question with an AI interviewer: https://sysround.com/practice/new?problem=car-rental-platform


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SysRound (https://sysround.com) is an AI practice tool for system design interviews. It has a voice or typed AI interviewer and a shared whiteboard. At the end, you get feedback on each skill and a model answer. The AI feedback can be wrong.