Correct, if all traffic goes to the WordPress site, then WordPress essentially owns the site, except if you have a reverse proxy intercepting traffic as it comes in, and deciding where it needs to go. One such reverse proxy is nginx... Or apache... Or lighttpd Think of it as such: The request for thesite.com comes in Nginx resolved this as a request that should go to WordPress, and thus kicks off the requisite php-fpm (or whatnot) processes to handle the request. Vs A request for thesite.com/forum comes in There is a rule saying anything that starts with /forum is actually NodeBB Nginx proxies the request to NodeBB to handle What is important to note is that how you configure nginx affects the routes on instances behind it. For example, if you configure nginx to serve NodeBB when /forum is accessed, then any /forum routes served by WordPress are inaccessible. Hope that helps explain it a bit!