Reverse proxy - variable

[cboyke]

I've seen this asked and answered many times - and I've tried many of the
suggestions posted, but still not able to get this to work.
I'm reverse-proxying to an internal IP inside an AWS VPC - eventually, I'd
like to use a JavaScript function to give the correct IP, but for now I'm
just hard-coding it in a variable.
I've tried all of the below, and none work:

server {
        listen 80;
        server_name myserver.com;
        location / {
            set $with_trailing_slash "http://172.31.17.123:8080/";
            #proxy_pass http://172.31.17.123:8080/;  #this works no
problem.
            #proxy_pass $with_trailing_slash;     # This gets to the
upstream but gives a 404;
            #proxy_pass $with_trailing_slash$request_uri;     # This spins
forever
            set $no_trailing_slash "http://172.31.17.123:8080";
            #proxy_pass $no_trailing_slash; #spins forever;
            #proxy_pass $no_trailing_slash$request_uri; #spins forever;
            set $just_ip 172.31.17.123;
            #proxy_pass http://$just_ip:8080/;        #404;
            #proxy_pass http://$just_ip:8080/$request_uri;     #spins
forever;
            set $ip_in_quotes "172.31.17.123";
            #proxy_pass http://$ip_in_quotes:8080/;   #404;
            #proxy_pass http://$ip_in_quotes:8080;   # spins forever;
            proxy_pass http://$iplookup:8080/;   # spins forever;
        }
}

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,282700,282700#msg-282700