DNS Caching Issue For community version

[RT.Nat]

Not clear regarding, " Also you might check using directly the hostname as
it might be possible that there is a bug when using variables." 

I tried adding the variable for resolving the dns but still the ip address
does not changes. Is there any other way? or is there any bug in my script.

resolver 8.8.8.8 valid=30s;
resolver_timeout 10s;
set $checkup "example.net";

location / {
    rewrite ^/(.*) /$1 break;
     proxy_pass https://$checkup:8080;
 }

even adding the following codes instead of the above proxy pass doesnt
work.

proxy_pass https://example.net:8080$request_uri;
proxy_pass https://example.net:8080;

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,266857,266880#msg-266880