proxy pass domain FROM default apache port 80 TO nginx on another port

Im still learning server things so hope the title is descriptive enough.

Basically i have sub.domain.com that i want to run on nginx at port 8090.

I want to leave apache alone and have it catch all default traffic at port 80.

so i am trying something with a virtual name host to proxy pass to sub.domain.com:8090, nothing working yet and go no idea what the right syntax could be.

any ideas? most of what i found was to pass TO apache FROM nginx, but i want to the do the opposite.

LoadModule proxy_module modules/mod_proxy.so

LoadModule proxy_http_module modules/mod_proxy_http.so

ProxyPreserveHost On

ProxyRequests Off

ServerName sub.domain.com

DocumentRoot /home/app/public

ServerAlias sub.domain.com

proxyPass / http://appname:8090/ (also tried localhost and sub.domain.com)

ProxyPassReverse / http://appname:8090/

when i do this i get

[warn] module proxy_module is already loaded, skippin

[warn] module proxy_http_module is already loaded, skipping

[error] (EAI 2)Name or service not known: Could not resolve host name sub.domain.com -- ignoring!

and yes, the app is working (i have it running on port 80 with another subdomain) and it works at sub.domain.com:8090