Design AirBnB or a Hotel Booking System

Design AirBnB or a Hotel Booking System

Requirements

Guests

• search rooms by locations, dates, and number of guests

• get room details(like picture, name, review, address, etc) and prices

• pay and book room from inventory by date and by room_id

  • checkout as a guest

  • user is logged in already

• notification via Email and mobile push notification

Hotel or Rental Admin

• manage room inventory and help the guest to check-in and check out

• housekeeper: clean up rooms routinely

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High-level architecture

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Detailed Design

Data Structure for User, Room and Booking

Ref: Designing a Data Model for a Hotel Room Booking System

• The basic tables are: reservation, guest and room.

• use status to represent the status of a room: EMPTY, RESERVED

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How to find available rooms?

Method 1: By location

• geo-search with spatial indexing

  • e.g. geo-hash or quad-tree

Method 2: By room metadata

• apply filters or search conditions when query the database

Method 3: By data-in and data-out availability

• option 1(recommended): for each room_id, create an entry for an occupied day. It will be easier to query unavailable slots by dates

• option 2: for each room_id, check all occupied_room from today.

  • transform the data structure to an array of occupied days

  • keep searching until got the available slots

  • this is time-consuming, so we can build the availability index

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External Hotel Supplier

• provide webhook callback APIs to external vendors to update status in the internal system

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Payment

Ref: Stripe Idempotency

• retry with idempotency to improve the success rate of the external calls and ensure no duplicate orders

Bookkeeping

• data model: double-entry bookkeeping
• sync data across transaction table and external banks and vendors

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Notification

The notification system is essentially a delayer scheduler (priority queue + subscriber) plus API integrations.

• For example, a daily cronjob will query the database for notifications to be sent out today and put them into the priority queue by date.

• The subscriber will get the earliest ones from the priority queue and send out if reaching the expected timestamp.

• Otherwise, put the task back to the queue and sleep to make the CPU idle for other work, which can be interrupted if there are new alerts added for today.