Some google results:
https://tenzer.dk/nginx-with-dynamic-upstreams/
http://stackoverflow.com/questions/24350124/port-number-getting-stripped-out-of-url
https://forum.nginx.org/read.php?2,239790,239794#msg-239794
https://tenzer.dk/nginx-with-dynamic-upstreams/
http://stackoverflow.com/questions/24350124/port-number-getting-stripped-out-of-url
https://forum.nginx.org/read.php?2,239790,239794#msg-239794