Breaking the Outbox — Five Edge Cases That Will Find You in Production

Duplicate delivery, ordering illusions, table bloat, competing publishers, and the cleanup problem. The outbox pattern works — until these arrive.

What happens when two instances of your publisher poll the outbox at the same time?

This was the question that woke me up — not literally at 3 AM, but close enough. We had deployed a second instance of the notification service for redundancy. A reasonable thing to do. Load balancer in front, health checks configured, infrastructure team satisfied. Nobody…