Auction System

Keywords: Tactical DDD, microservice, kotlin, spring-boot, Hexagonal-Architecture, SOLID, Domain-Driven Design, functional-programming, Testing, Event-Driven Architecture, Domain-Events, Kafka, MongoDB, Transactional-outbox, optimistic-locking

Problem

Design and implement an online auction system that allows buyers to participate on auctions through digital means, rather than being at a physical location.

Functional requirements

• Sellers can post any item for auction at any time from their catalog, with an initial price, a minimal bid and an opening date-time.
• An item can not be for an auction twice, unless it was not sold in a previous action.
• An auction can not be changed, only cancelled, but only after 5 min of creation.
• An auction will be on a preview status for a while, between 1 day to 7 days, allowing potential buyers to take a look beforehand.
• Once an auction is open, bidders can bid for the item.
• A Bidder wins an item if there are no higher bids in the next 20 min.
• An auction will expire if there aren't any bidders in a period of 1h.
• Bidders can bid on any existing item any number of times.
• Bids are only allowed during opening time.
• The platform would allow auto-bidding up to a limit, increasing automatically your bid every time someone outbids you.

Scope

The scope of the system should be auctions, we will work with the assumption that we will have other systems in place for:

• Catalog
• User lifecycle
• ...

Design only the Backend part, let's skip all the FE side.

Non Functional Requirements

• Low Latency
• High Availability
• Highly consistent

Estimated workloads

• 10M auctions added every day
• 100M requests to bid on these items