How One Team Fixed Race Conditions Caused by Duplicate Webhook Deliveries

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An engineering team discovered a critical race condition in production after duplicate webhooks bypassed application-level checks and left their database in an inconsistent state. The problem stemmed from multiple container instances simultaneously processing identical events, both passing validation and writing to the database at the same time. To resolve this, the team implemented an Idempotent Consumer Pattern using two defensive layers: a Redis distributed lock using the atomic SETNX command with a 30-second TTL, and a unique-constraint-backed idempotency keys table in their relational database. The database layer ensures that any duplicate slipping past Redis triggers a UniqueConstraintViolationException and rolls back the entire transaction atomically. Stress tests with 10,000 concurrent duplicate requests per second confirmed the solution achieved full data consistency with negligible performance impact.

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