Design a Book Price Aggregator
Design a book purchasing marketplace service that acts as an intermediary between customers and hundreds of partner bookstores. This service will facilitate finding and purchasing books based on customer-defined criteria.
Customer Input
For each purchase request, a customer provides:
- An International Standard Book Number (ISBN).
- A bid price, representing the maximum price they are willing to pay.
- A payment method.
Core Functionality
Your system must asynchronously fan out requests to hundreds of partner bookstores to query their available inventory and current prices for the specified ISBN.
System Behavior
Based on the responses from partner bookstores, the system must exhibit the following behavior:
- Successful Purchase: If at least one bookstore has inventory and the lowest available price found across all responding partners is less than or equal to the customer's bid price, the system must place an order with that specific bookstore.
- Price Exceeds Bid: If bookstores have inventory but the lowest available price found is higher than the customer's bid price, the system should return this lowest available price to the customer, indicating that a purchase could not be made at their desired price.
- Unavailable: If no bookstore has inventory for the given ISBN, the system must notify the customer that the book is unavailable.
Key Design Considerations
Your design discussion should deeply explore the following aspects:
- Resilience: How to tolerate downstream bookstore failures, slow responses, and timeouts.
- Partial Results: Strategies for aggregating results when not all partner bookstores respond within acceptable limits.
- Circuit Breakers: Whether and how to implement circuit breakers to protect against failing or slow partners.
- Scalability: How to scale the system effectively when facing a large volume of external calls to partner APIs.
- Efficiency: Methods to reduce the number of downstream calls, including caching, Time-To-Live (TTL) mechanisms, request coalescing, and protection against the "thundering herd" problem.
- Consistency: How to handle consistency challenges when ordering a book and charging a customer are two separate external calls.
- Transactional Integrity: The decision between ordering first or charging first, strategies for recovery if the system crashes midway through this process, and mechanisms to prevent duplicate charges or duplicate orders.
AI interview prep
Core dilemma
Balancing real-time performance and resilience against hundreds of unreliable external dependencies, while maintaining transactional integrity and preventing financial discrepancies (duplicate charges/orders) in a high-volume, distributed environment.
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 Book Price Aggregator
Design a book purchasing marketplace service that acts as an intermediary between customers and hundreds of partner bookstores. This service will facilitate finding and purchasing books based on customer-defined criteria.
Customer Input
For each purchase request, a customer provides:
- An International Standard Book Number (ISBN).
- A bid price, representing the maximum price they are willing to pay.
- A payment method.
Core Functionality
Your system must asynchronously fan out requests to hundreds of partner bookstores to query their available inventory and current prices for the specified ISBN.
System Behavior
Based on the responses from partner bookstores, the system must exhibit the following behavior:
- Successful Purchase: If at least one bookstore has inventory and the lowest available price found across all responding partners is less than or equal to the customer's bid price, the system must place an order with that specific bookstore.
- Price Exceeds Bid: If bookstores have inventory but the lowest available price found is higher than the customer's bid price, the system should return this lowest available price to the customer, indicating that a purchase could not be made at their desired price.
- Unavailable: If no bookstore has inventory for the given ISBN, the system must notify the customer that the book is unavailable.
Key Design Considerations
Your design discussion should deeply explore the following aspects:
- Resilience: How to tolerate downstream bookstore failures, slow responses, and timeouts.
- Partial Results: Strategies for aggregating results when not all partner bookstores respond within acceptable limits.
- Circuit Breakers: Whether and how to implement circuit breakers to protect against failing or slow partners.
- Scalability: How to scale the system effectively when facing a large volume of external calls to partner APIs.
- Efficiency: Methods to reduce the number of downstream calls, including caching, Time-To-Live (TTL) mechanisms, request coalescing, and protection against the "thundering herd" problem.
- Consistency: How to handle consistency challenges when ordering a book and charging a customer are two separate external calls.
- Transactional Integrity: The decision between ordering first or charging first, strategies for recovery if the system crashes midway through this process, and mechanisms to prevent duplicate charges or duplicate orders.