title: How nginx reload work ? why it is zero-downtime
body: <p>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 . </p>
  
  <p>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 .</p>