Webhooks & Message Queues - Events and Async Integration Beyond Request/Response

How services talk to each other when one of them isn't waiting for an answer: webhooks let another system call your URL when something happens, and message queues let your own services hand off work to be done later.

1. Push vs Pull: Webhooks Polling means asking 'any news?' over and over and mostly hearing 'no'; a webhook flips it so the other service POSTs to your URL the moment something happens - and because anyone can POST to that URL, you must verify the request is genuine.
2. Message Queues A message queue is a shared to-do list between your services: a producer drops a message and moves on, a consumer picks it up when it's ready - which decouples them, absorbs traffic spikes, and lets work survive even if the consumer is temporarily down.
3. When to Use Which (and the Gotchas) Webhooks are for cross-system event notifications; queues are for internal async work and smoothing load - and both deliver at-least-once, so the same event can arrive twice, which is why your handlers must be idempotent. Plus retries, ordering, and dead-letter queues, gently.