What does nginx smooth restart mean?

Question

Doesn’t it mean to stop the service?

Answer 1

It should mean reloading the configuration file, or upgrading nginx without stopping the business.
The general principle is that nginx will start a new worker with a new configuration file, and then slowly stop the old configuration worker that has processed the request.

Answer 2

nginx runs a new worker process and gracefully shuts down the old worker process, notifying the worker process to close the listening socket but continue to serve currently connected clients. After all client services are completed, the old worker process is shut down. If application of the new configuration file fails, nginx will continue to work using the old configuration file.