Normal use of proxy_pass

server {
    proxy_pass http://upstream-host.com:8080;
}

Instead, use a variable in your nginx config to disable nginx caching the DNS for upstream-host.com like this:

server {
    ...
    resolver 127.0.0.1;
    set $backend "http://upstream-host.com:8080";
    proxy_pass $backend;
    ...
}

When nginx is running inside a Docker container then you need to use:

    resolver 127.0.0.11 ipv6=off;