eBay / Auction System — Simple

Problem statement (interviewer prompt)

Design an online auction system (eBay): listings with bidding, proxy bidding (auto-rebid up to a max), live leaderboard, anti-snipe extensions, winner determination, and payment + shipping handoff. Strictly serialise bids per listing.

flowchart LR
  S[Seller]
  L[Listing Service]
  A[Auction Engine]
  B[Bidder]
  PAY[Payment]
  S --> L
  B --> A
  L --> A
  A --> PAY

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class S,L,A,B,PAY service;