StubHub·Software Engineer·Onsite - System Design / Architecture
Jun 2026
StubHub system design round focused entirely on building a real-time internal chat platform, plus a bonus workflow question about re-engaging inactive users via email. Pretty dense for a single session but the scope made sense given the role.
- Design an internal chat system for an event marketplace company that supports real-time one-to-one messaging, persistent WebSocket connections, presence tracking, and conversation history.
- How would you handle message delivery for offline users, and what storage approach would you use for chat history?
- Walk through how bidirectional WebSocket communication gets routed across multiple servers when the sender and recipient are connected to different nodes.
- Within the same platform, design a workflow that automatically sends an email to customers who haven't logged in for 10 days.
“I started with the WebSocket layer and worked outward, which felt right but I spent too long on connection management before touching storage.” The rest of the author's notes on Software Engineer interview at StubHub, Onsite - System Design / Architecture round, covers how they worked through the question, what the panel pushed back on, and what they would do differently.
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