I have a ubuntu server running a few apache websites. I want to run a nodejs app on the same server. I have the app running on the server now out of port 3000 (www.example.c
First of all, you should to install mod_proxy and mod_proxy_http.
Then you can use something like the following configuration:
<VirtualHost *:80>
  ServerAdmin spam@example.com
  ServerName example.com
  ServerAlias www.example.com 
  ProxyRequests off
  <Proxy *>
    Order deny,allow
    Allow from all
  </Proxy>
  <Location />
    ProxyPass http://localhost:3000/
    ProxyPassReverse http://localhost:3000/
  </Location>
</VirtualHost>