Design a Large-Scale Online Ticketing System
Design an online ticketing system, similar to platforms like Ticketmaster, capable of handling extremely high concurrency for popular events where a massive number of users attempt to purchase tickets simultaneously.
The system must fulfill the following core requirements:
1. High-Concurrency Ticket Purchase
- The system must support tens or hundreds of thousands of users attempting to buy tickets for the same event at the exact same moment.
- It is critical to prevent overselling of seats while maintaining low user-facing latency during the purchase flow.
2. Inventory and Seat Management
- Events can feature complex seating arrangements, including multiple sections and individual seat-level inventory.
- When a user initiates the checkout process, selected seats must be temporarily reserved for a short duration (e.g., 5 minutes).
- These reservations must automatically expire if the payment is not completed within the allotted time, returning the seats to the general available pool.
3. Payment Timeout and Guarantee
- Integration with external payment providers is required, which may introduce processing times of several seconds.
- A fundamental guarantee: if payment successfully completes within the allowed reservation window, the user must always receive tickets for the seats they had reserved ("payment implies ticket issuance").
- Conversely, if payment fails or times out, the reserved seats must be promptly released back into inventory.
4. Sold-Out Handling and Waitlist
- When an event's immediate inventory is exhausted, users should have the option to join a waitlist.
- If previously held seats become available (e.g., due to reservation or payment expiration), users on the waitlist must be automatically offered these seats in a fair, ordered manner.
- The design should consider mechanisms for notifying waitlist users and defining a reasonable timeframe for them to claim newly available tickets.
5. Consistency and Correctness
- The system must rigorously prevent double-selling of any seat, even under extreme load and across distributed deployments.
- Candidates must explain their approach to handling race conditions (e.g., multiple users attempting to reserve the same seat simultaneously) and detail the consistency guarantees provided by their design.
6. Scalability and Performance
- The architecture must be horizontally scalable to accommodate large-scale ticket on-sales.
- The design should account for diverse read/write patterns, including browsing events, selecting seats, creating reservations, performing checkout, and issuing tickets.
- A comprehensive data model and storage strategy for events, seats, reservations, and orders must be proposed.
7. APIs and Components
- Describe the primary services and components of the system (e.g., API gateway, event catalog service, inventory/reservation service, payment service, waitlist service).
- Sketch the key APIs required for core functionalities such as searching events, retrieving seating maps, creating reservations, confirming purchases (payment), canceling reservations, and joining a waitlist.
The final design should be presented end-to-end, covering data modeling, concurrency control, reservation and expiration logic, integration with payment providers, waitlist behavior, and strategies for testing and monitoring the system in a production environment.
AI interview prep
Core dilemma
Balancing the absolute consistency required for preventing overselling of unique, limited inventory (seats) with the extreme write throughput and low latency demands of a flash sale scenario, all within a distributed system.
3 tradeoffs and 3 stress tests locked
Interview prep
Unlock the interviewer X-Ray rubric, tradeoff matrix, stress tests, clarifying questions, and key concepts.
Design a Large-Scale Online Ticketing System
Design an online ticketing system, similar to platforms like Ticketmaster, capable of handling extremely high concurrency for popular events where a massive number of users attempt to purchase tickets simultaneously.
The system must fulfill the following core requirements:
1. High-Concurrency Ticket Purchase
- The system must support tens or hundreds of thousands of users attempting to buy tickets for the same event at the exact same moment.
- It is critical to prevent overselling of seats while maintaining low user-facing latency during the purchase flow.
2. Inventory and Seat Management
- Events can feature complex seating arrangements, including multiple sections and individual seat-level inventory.
- When a user initiates the checkout process, selected seats must be temporarily reserved for a short duration (e.g., 5 minutes).
- These reservations must automatically expire if the payment is not completed within the allotted time, returning the seats to the general available pool.
3. Payment Timeout and Guarantee
- Integration with external payment providers is required, which may introduce processing times of several seconds.
- A fundamental guarantee: if payment successfully completes within the allowed reservation window, the user must always receive tickets for the seats they had reserved ("payment implies ticket issuance").
- Conversely, if payment fails or times out, the reserved seats must be promptly released back into inventory.
4. Sold-Out Handling and Waitlist
- When an event's immediate inventory is exhausted, users should have the option to join a waitlist.
- If previously held seats become available (e.g., due to reservation or payment expiration), users on the waitlist must be automatically offered these seats in a fair, ordered manner.
- The design should consider mechanisms for notifying waitlist users and defining a reasonable timeframe for them to claim newly available tickets.
5. Consistency and Correctness
- The system must rigorously prevent double-selling of any seat, even under extreme load and across distributed deployments.
- Candidates must explain their approach to handling race conditions (e.g., multiple users attempting to reserve the same seat simultaneously) and detail the consistency guarantees provided by their design.
6. Scalability and Performance
- The architecture must be horizontally scalable to accommodate large-scale ticket on-sales.
- The design should account for diverse read/write patterns, including browsing events, selecting seats, creating reservations, performing checkout, and issuing tickets.
- A comprehensive data model and storage strategy for events, seats, reservations, and orders must be proposed.
7. APIs and Components
- Describe the primary services and components of the system (e.g., API gateway, event catalog service, inventory/reservation service, payment service, waitlist service).
- Sketch the key APIs required for core functionalities such as searching events, retrieving seating maps, creating reservations, confirming purchases (payment), canceling reservations, and joining a waitlist.
The final design should be presented end-to-end, covering data modeling, concurrency control, reservation and expiration logic, integration with payment providers, waitlist behavior, and strategies for testing and monitoring the system in a production environment.