Nginx - Solution for 10060: A connection attempt failed because the connected party did not properly respond

I was in the process of setting up Nginx to serve as the reverse proxy for Nexus Repository Manager OSS. However, the Nexus repository started loading really slowly post this and used to repeatedly display disconnected and reconnected messages. The Nginx log file used to log the below error -

<timestamp> [error] 3240#3632: *1 upstream timed out (10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond) while connecting to upstream, client: <ip address="">, server: <fqdn>, request: "GET /nexus HTTP/1.1", upstream: "http://[::1]:8081/nexus", host: "<fqdn>"

My nginx.conf for this context path was -

location /nexus {   

proxy_set_header        Host $host:$server_port;    proxy_set_header        X-Real-IP $remote_addr;    proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;   

proxy_set_header        X-Forwarded-Proto $scheme;    proxy_redirect http:// https://;   

proxy_pass http://<fqdn>:8081/nexus; # though this was the same VM, I used FQDN here

}

After spending a significant amount of time, I finally came across a really simple but non-obvious solution here. It was to change proxy_pass to;

proxy_pass http://127.0.0.1:8081/nexus;

Quoting from the linked document -

There might also be an issue when using domain names which are external while you are internal to Nginx, ea. All traffic going out through a router and back in again, use a local DNS (or your ‘host’ file to keep such traffic local) 

Now the Nexus repository does not have any access issues. Loads blazing fast.