Design a Hotel & Flight Booking System

Geo, Maps & MarketplacesHarddesign-booking-system

Design a Hotel & Flight Booking System

Design inventory where overselling is unacceptable: holds that expire, searches across a huge date-and-price space, and a payment step that happens after the seat is already claimed.

Inventory ReservationOptimistic ConcurrencyTwo-Phase BookingIdempotency

Traffic & Capacity Estimates:

10M properties · 100k searches/second · 5k bookings/second · zero overselling

Functional Requirements

•Search availability across dates, locations, and prices with faceted filters.
•Place a temporary hold on inventory during checkout, expiring automatically if payment stalls.
•Confirm a booking atomically with payment capture, or release the hold cleanly.
•Support cancellation, modification, and refund against the original inventory.

Non-Functional Requirements

•Never sell the same room or seat twice, even under concurrent checkout.
•Search results in under 300ms across a very wide parameter space.
•Inventory state must be recoverable and auditable after any partial failure.

Back-of-the-Envelope Math

10M properties * 365 dates * 20 room types = 73B availability records — the search index must be denormalized aggressively.
Holds at 5k bookings/s with a 15-minute TTL means up to 4.5M live holds at any moment.

Key Architectural Trade-offs

Pessimistic locking on inventory rows guarantees no oversell and serializes hot properties; optimistic concurrency with a version check scales and pushes retries to the client.
Search reads from a denormalized, slightly stale index while booking writes against the authoritative store — the gap is why 'this room was just taken' exists as a user-facing state.
Holds convert availability into a distributed-lock problem with a TTL; too short frustrates checkout, too long hides sellable inventory.

Click or drag a component onto the canvas, then connect the handles to draw the data flow.

3 nodes · 2 edges

Components · 35

Client & Edge4

Compute & Gateway7

Storage & Caching11

Messaging & Streaming6

Coordination & Ops5

Intelligence2

React Flow