Just in case you run into this.
Installed Nginx on mostly vanilla 14.04 trusty Ubuntu. Just walking through the simple Nginx (1.6.0) setup docs with a tail -f running on logs I was seeing the below inconsistent error while using the proxy_pass setting in my server directive.
==> /var/log/nginx/error.log <==
2014/05/11 14:31:50 [error] 4003#0: *5 connect() failed (111: Connection refused) while connecting to upstream, client: , server: , request: “GET / HTTP/1.1”, upstream: “http://[::1]:8080/”, host: “”
When I finally realized I was seeing an issue with IPv6, which I don’t use, I disabled it and the error went away.
Disable IPv6 on Ubuntu: