I've never set up a proxy before. I'm using shared hosting, so to set Apache directives, I need to use .htaccess. Can I use .htaccess to do something like below? Any limitations?
ProxyRequests Off
ProxyPass /img/ http://internal.example.com/img/
ProxyPass /app/ http://internal.example.com/app/
ProxyPassReverse / http://internal.example.com/
You cannot use a ProxyPass in an htaccess file. The documentation says it is only applicable in the context:
Context: server config, virtual host, directory
which excludes htaccess (you can't have a <Directory> block in htaccess). However, you can use a ProxyPassReverse to internally rewrite the Location field of proxied requests that cause a redirect. You'll just need to use mod_rewrite's P flag to proxy instead of ProxyPass. So something like:
RewriteEngine On
RewriteRule ^/?img/(.*)$ http://internal.example.com/img/$1 [L,P]
RewriteRule ^/?app/(.*)$ http://internal.example.com/app/$1 [L,P]
ProxyPassReverse / http://internal.example.com/
Just to be clear, you cannot use ProxyPass or ProxyPassReverse in the htaccess file, but you can use ProxyPassReverse with mod_rewrite rules that utilize the P flag.