I have Nginx server configured with couple of backend servers with keepalive connections enabled.

I am trying to understand what will be the Nginx's behaviour in case the connection is closed by an upstream server legitimately when Nginx is trying to send a new request exactly at the same time. In this race condition, does Nginx re-try the request internally or does it return an error code?

In case Nginx needs to be forced to retry, should I be using proxy_next_upstream? My understanding is that this setting will make the request re-tried on the next server in the upstream block. On the same note, how do I force the retry on the failed server first to avoid cache misses.

Thanks,
Gopala