Is it possible to use "%{HTTP_HOST}" in ProxyPass? - apache

Question

I'm trying to implement a transparent proxy using apache2 and mod_proxy that for now - doesn't do anything. just forwards the traffic to the correct "host".
I don't want it to be host-dependant - but dynamic so it'll work for all hosts.
I tried to do this:
RewriteEngine on
RewriteLogLevel 5
RewriteLog "/var/log/apache2/rewrite.log"
RewriteRule ^(.*)$ $1
ProxyPass / http://$1
I also tried several other approaches (none worked).
Is there any way I can access the "host" from the header and use it in the ProxyPass directive?
In nginx I would use $host, $remote_addr, etc.. any way to replace that on apache?
What I need is to be able to access %{HTTP_HOST}, %{REQUEST_URI} and %{SERVER_PORT} inside the ProxyPass command.

Answer 1

To use Apache ProxyPass directives with dynamic hostnames you will need to also use ModRewrite.
Objective
All requests to the virtualhost will ProxyPass and ProxyPassReverse (also known as an "Apache Gateway") to the %{HTTP_HOST}
The only reason this would make sense to do is if you have localhost entries on the apache server for specfic host names
Examples
Localhost File
10.0.0.2 foo.bar.com
10.0.0.3 bar.bar.com
How it works
The client makes a request to foo.bar.com (dnslookup is a public IP... YOUR APACHE SERVER)
Your apache server has a localhost entry of 10.0.0.2 for foo.bar.com (some other server on your network)
The request goes through ModRewrite and /path1 is appended, then handed off to ProxyPass and ProxyPassReverse
ProxyPass and ProxyPassReverse hand the call off to foo.bar.com at ip 10.0.0.2
Client requests foo.bar.com ---reverse proxies to----> foo.bar.com/path1 (on some OTHER internal server)
Apache Configuration
<VirtualHost *:443>
Servername *
# Must not contain /path1 in path (will add /path1)
RewriteEngine on
RewriteCond %{REQUEST_URI} !^/path1/.*
RewriteRule ^/(.*) https://%{HTTP_HOST}/path1$1 [NC,R=302,L]
# Must contain /path1 in path (will send request to the proxy)
RewriteEngine On
RewriteOptions Inherit
RewriteCond %{REQUEST_URI} ^/path1/.*
RewriteRule ^(.*)$ https://%{HTTP_HOST}$1 [NC,P]
SSLEngine on
SSLProxyEngine On
ProxyRequests Off
ProxyPass / https://$1/
ProxyPassReverse / https://$1/
ProxyPreserveHost On
###################
# SSL Constraints #
###################
SSLProtocol -ALL +SSLv3 +TLSv1
# Choose cipher suites
SSLHonorCipherOrder On
SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:!LOW:!SSLv2:!EXPORT
# SameOrigin The page can only be displayed in a frame on the same origin as the page itself
Header set X-Frame-Options SAMEORIGIN
SSLCertificateFile /etc/apache2/example.crt
SSLCertificateKeyFile /etc/apache2/example.key
SSLCertificateChainFile /etc/apache2/gd_bundle.crt
SetOutputFilter INFLATE;proxy-html;DEFLATE
</VirtualHost>

Answer 2

Just answering my own question:
I was missing 2 things:
the configuration should be:
RewriteEngine On
RewriteRule ^(.*)$ http://%{HTTP_HOST}$1 [P]
Not to forget to enable inherit in the virtual directory:
RewriteEngine On
RewriteOptions Inherit

Answer 3

You should read this page if you haven't done it already :
https://httpd.apache.org/docs/2.2/mod/mod_proxy.html#forwardreverse
I think the ProxyRequests directive is what you are looking for.