Design a Real-time Auction Bidding System

To design a real-time auction system for Meta, I would start by defining strict non-functional requirements. Given the high-frequency nature, we need sub-10 millisecond latency from bid submission to validation. I propose an architecture where client requests hit a global load balancer routing to regional API gateways. These gateways push bid events into a partitioned message queue like Apache Kafka to decouple ingestion from processing. This handles the write-heavy spike without blocking the UI. For the core logic, each auction shard maintains a priority queue sorted by timestamp and bid value. When a new bid arrives, we check if it exceeds the current highest bid. To avoid starvation, we strictly enforce that earlier timestamps with slightly lower amounts are not discarded; instead, they remain visible as valid offers until overtaken. We use Redis as a low-latency cache for the current state of active auctions, allowing O(1) read access for bidders checking the leading price. For final result confirmation, we implement a deterministic leader election per auction instance. Once the timer expires, the system processes all buffered messages in order, calculates the winner, and publishes a 'AuctionEnded' event. This ensures that even if network partitions occur, the outcome remains consistent across replicas, aligning with Meta's focus on robust, scalable infrastructure that prioritizes user experience through reliability.