A field guide to receiving webhooks reliably: verify signatures on the raw body, respond fast, queue the work, deduplicate by event ID, tolerate out-of-order delivery, replay safely and monitor the whole pipeline. With code you can adapt.
Every system that needs to tell another system that something happened ends up choosing between polling, webhooks, WebSockets and a message broker. A practical comparison by who connects to whom, delivery guarantees, firewalls, fan-out and cost, with the failure mode of each and the combination we use most.
A slow accounting API pushed our PayPal webhook handler past the nginx timeout. PayPal saw a 504 and retried, while the first request was still running, and 41 wallets were topped up twice. Postmortem plus the idempotent design we moved to.
After a harmless-looking Express refactor, every Stripe webhook failed verification and paid bookings stayed pending. A global JSON parser consumed the body before constructEvent saw it. How we found it, fixed the route and replayed the missed events.