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?