Setup (Apache: The Definitive Guide, 3rd Edition)

You now have to tell your browser that you are going to be accessing the Web via a proxy. For example, in Netscape click on Edit

Preferences

Advanced

Proxies tab

Manual Proxy Configuration. Click on View,and in the HTTP box enter the IP address of our proxy, which is on the same network, 192.168.123, as our copy of Netscape:

9.5.1. Reverse Proxy

This section explains a configuration setup for proxying your backend mod_perl servers when you need to use virtual hosts. See perl.apache.org/guide/scenario.html, from which we have quoted freely. While you are better off getting it right in the first place (i.e. using different URLs for the different servers), there are at least three reasons you might want to rewrite:

Because you didn't think of it in the first place and you are now fighting fires.
Because you want to save page size by using relative URLs instead of full ones.
You might improve performance by, for instance, caching the results of expensive CGIs.

The term virtual host refers to the practice of maintaining more than one server on one machine, as differentiated by their apparent hostname. For example, it is often desirable for companies sharing a web server to have their own domains, with web servers accessible as www.company1.com and www.company2.com, without requiring the user to know any extra path information.

One approach is to use a unique port number for each virtual host at the backend server, so you can redirect from the frontend server to localhost:1234 and name-based virtual servers on the frontend, though any technique on the frontend will do.

If you run the frontend and the backend servers on the same machine, you can prevent any direct outside connections to the backend server if you bind tightly to address 127.0.0.1 (localhost), as you will see in the following configuration example.

This is the frontend (light) server configuration:

<VirtualHost 10.10.10.10>
  ServerName www.example.com
  ServerAlias example.com
  RewriteEngine On
  RewriteOptions 'inherit'
  RewriteRule \.(gif|jpg|png|txt|html)$ - [last]
  RewriteRule ^/(.*)$ http://localhost:4077/$1 [proxy]
</VirtualHost>
<VirtualHost 10.10.10.10>
  ServerName foo.example.com
  RewriteEngine On
  RewriteOptions 'inherit'
  RewriteRule \.(gif|jpg|png|txt|html)$ - [last]
  RewriteRule ^/(.*)$ http://localhost:4078/$1 [proxy]
</VirtualHost>

This frontend configuration handles two virtual hosts: www.example.com and foo.example.com. The two setups are almost identical.

The frontend server will handle files with the extensions .gif, .jpg, .png, .txt, and .html internally; the rest will be proxied to be handled by the backend server.

The only difference between the two virtual-host settings is that the former rewrites requests to port 4077 at the backend machine and the latter to port 4078.

If your server is configured to run traditional CGI scripts (under mod_cgi), as well as mod_perl CGI programs, then it would be beneficial to configure the frontend server to run the traditional CGI scripts directly. This can be done by altering the gif|jpg|png|txt Rewrite rule to add |cgi at the end if all your mod_cgi scripts have the .cgi extension, or by adding a new rule to handle all /cgi-bin/* locations locally.

Here is the backend (heavy) server configuration:

Port 80

PerlPostReadRequestHandler My::ProxyRemoteAddr

Listen 4077
<VirtualHost localhost:4077>
  ServerName www.example.com
  DocumentRoot /home/httpd/docs/www.example.com       
  DirectoryIndex index.shtml index.html
</VirtualHost>

Listen 4078
<VirtualHost localhost:4078>
  ServerName foo.example.com
  DocumentRoot /home/httpd/docs/foo.example.com
  DirectoryIndex index.shtml index.html
</VirtualHost>

The backend server knows to tell to which virtual host the request is made, by checking the port number to which the request was proxied and using the appropriate virtual host section to handle it.

We set Port 80 so that any redirects use 80 as the port for the URL, rather than the port on which the backend server is actually running.

To get the real remote IP addresses from proxy, My::ProxyRemoteAddr handler is used based on the mod_proxy_add_forward Apache module. Prior to mod_perl 1.22, this setting must have been set per-virtual host, since it wasn't inherited by the virtual hosts.

The following configuration is yet another useful example showing the other way around. It specifies what is to be proxied, and then the rest is served by the frontend:

  RewriteEngine     on
  RewriteLogLevel   0
  RewriteRule       ^/(perl.*)$  http://127.0.0.1:8052/$1   [P,L]
  NoCache           *
  ProxyPassReverse  /  http://www.example.com/

So we don't have to specify the rule for static objects to be served by the frontend, as we did in the previous example, to handle files with the extensions .gif, .jpg, .png and .txt internally.

9.5. Setup

9.5.1. Reverse Proxy