How nginx reload work ? why it is zero-downtime

Question

refer to nginx official docs . the reload command of nginx is for reload of configuration files ，and during the progress , there's no downtime of the service .

i've learned that it wait requests that already connected until it finished ,and stop accept any new request . the idea is cool , but how does it deal with the keep-live connections ? because those long-live connections won't close and there continuous request comes along .

Answer 1

Here's the summary:

http://nginx.org/en/docs/control.html

The master process first checks the syntax validity, then tries to apply new configuration. If this succeeds, it starts new worker processes, and sends messages to old worker processes requesting them to shut down gracefully.

That means it would keep older processes handling unclosed connections while having new processes working according to the updated configuration. From this perspective connections with keep-alive are no different from other unclosed connections.

In versions prior to 1.11.11 such "old" processes could hang indefinitely long (according to @Alexey, haven't checked it though), from 1.11.11 there’s a configuration setting controlling this http://nginx.org/en/docs/ngx_core_module.html#worker_shutdown_timeout