How does Nginx handle the request of the upstream server when it is marked as `down`?

[HUMing]

For a simple Nginx configuration like this:
For a simple Nginx configuration like this:

upstream myservers {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
}
server {
    listen       80;
    location / {
        proxy_pass http://myservers;
    }
I have two questions related zero downtime of the application:

If I change the configuration to mark the first server server 127.0.0.1:3000
as down, I assume that no new request will go to that server, but what about
the current request that is handled by the upstream server? Does Nginx can
still return valid response to end user for that request?

If I remove the first server server 127.0.0.1:3000 and reload the
configuration, what about the current request that is handled by this
upstream server?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,257985,257985#msg-257985