Guide to building idempotent webhook handlers using Node.js and Postgres

An idempotent webhook handler ensures duplicate event processing yields the same result as a single one. This is crucial because providers like Stripe guarantee 'at-least-once' delivery, meaning events can arrive multiple times or out of order. A robust method involves verifying the webhook signature using the raw request body and storing each event's ID in a uniquely constrained database table. Finally, the application's business logic must be executed within the same database transaction as the event record insertion. This approach prevents race conditions and common bugs like issuing double credits or sending duplicate emails.