Design Auction System
Design an Online Auction System that allows users to list items, place bids in real-time, track highest bids, and automatically determine winners when auctions end.
An Online Auction System is a digital platform that facilitates the buying and selling of items through competitive bidding, typically over a fixed time window. Sellers can list products for auction, and buyers can place incremental bids to compete for ownership.
At the end of the auction period, the highest bidder wins, and the system finalizes the transaction. Examples of such platforms include eBay, Sotheby’s, and GovDeals.
In this chapter, we will explore the low-level design of an online auction system in detail.
Let's start by clarifying the requirements:
1. Clarifying Requirements
Before starting the design, it's important to ask thoughtful questions to uncover hidden assumptions, clarify ambiguities, and define the system's scope more precisely.
Here is an example of how a conversation between the candidate and the interviewer might unfold:
Candidate: Can a user place bids on multiple items simultaneously?
Interviewer: Yes, users should be able to participate in multiple ongoing auctions at the same time.
Candidate: How is the winner of an auction determined? Is it simply the highest bid at the end time?
Interviewer: Correct. The user with the highest bid when the auction ends wins the item. In case of a tie, the earliest bid should be considered the winner.
Candidate: Should users receive notifications when they’re outbid or when an auction they’re involved in ends?
Interviewer: Yes, users should be notified when they’re outbid, and when an auction they’re participating in ends.
Candidate: Should we keep a record of all bids for an item?
Interviewer: Yes, the system should maintain a complete bid history for each auction item.
Candidate: What about post-auction activities like payment processing and shipping?
Interviewer: Let's consider those out of scope. The system's responsibility ends once the auction is closed and a winner is declared.
After gathering the details, we can summarize the key system requirements.
1.1 Functional Requirements
- Allow users to create and list auction items with a title, description, starting price, and end time
- Allow users to place bids on active auctions
- Support concurrent bidding on multiple items by the same or different users
- Determine the winner based on the highest bid at auction end; resolve ties by earliest bid.
- Notify users when they are outbid or when the auction ends
- Prevent bids once the auction has ended.
- Maintain a complete bid history for each auction item.
1.2 Non-Functional Requirements
- Concurrency: The system must be thread-safe to handle multiple simultaneous bids on the same auction without data integrity issues.
- Modularity: The system should follow object-oriented design with clear separation of concerns.
- Reliability: The mechanism for closing auctions at their specified end time must be reliable and function automatically.
- Maintainability: The codebase should be clean, testable, and easy to enhance or debug.
- Extensibility: The design should be modular, making it easy to add new features in the future, such as different auction types or user roles.
- Simplified Interface: The system should provide a simple, high-level API for clients to perform key actions like creating an auction or placing a bid, hiding the underlying complexity.