12.10.1. Virtual Host Flavors

12.10.2. Dual-Server Virtual Host Configuration

SSL-enabled sites cannot use this scheme, however. This is because when using SSL, all HTTP traffic is encrypted, and this includes the request's Host: header. This header is unavailable until the SSL handshake has been performed, and that in turn requires that the request has been dispatched to the appropriate virtual host, because the SSL handshake depends on that particular host's SSL certificate. For this reason, each SSL-enabled virtual host needs its own, unique IP address. You can still use name-based virtual hosts along with SSL-enabled virtual hosts in the same configuration file, though.

For the backend mod_perl-enabled server, we recommend using port-based virtual hosts using the IP address 127.0.0.1 (localhost). This enforces the fact that this server is accessible only from the frontend server and not directly by clients.

12.10.3. Virtual Hosts and Main Server Interaction

In the following example, we use the PerlSetupEnv directive to turn off environment population for all virtual hosts, except for the www.example.com virtual host, which needs it for its legacy CGI scripts running under Apache::Registry:

PerlSetupEnv Off

Listen 8001
<VirtualHost 127.0.0.1:8001>
    ServerName www.example.com
    PerlSetupEnv On
</VirtualHost>

12.10.4. Frontend Server Configuration

Listen            192.168.1.2:80
NameVirtualHost   192.168.1.2:80

Replace 192.168.1.2 with your server's public IP address.

LogFormat "%v %h %l %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-agent}i\""

The log format used is the Common Log Format prefixed with %v, a token representing the name of the virtual host. Using a combined log common to all virtual hosts uses fewer system resources. The log file can later be split into seperate files according to the prefix, using splitlog or an equivalent program.

The following are global options for mod_rewrite shared by all virtual hosts:

RewriteLogLevel       0
RewriteRule \.(gif|jpg|png|txt|html)$ - [last]

This turns off the mod_rewrite module's logging feature and makes sure that the frontend server will handle files with the extensions .gif, .jpg, .png, .txt, and .html internally.

If your server is configured to run traditional CGI scripts (under mod_cgi) as well as mod_perl CGI programs, 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|html) rewrite rule to add cgi if all your mod_cgi scripts have the .cgi extension, or by adding a new rule to handle all /cgi-bin/* locations internally.

The virtual hosts setup is straightforward:

##### www.example.com
<VirtualHost 192.168.1.2:80>
    ServerName      www.example.com
    ServerAdmin     webmaster@example.com
    DocumentRoot    /home/httpd_docs/htdocs/www.example.com

    RewriteEngine       on
    RewriteOptions      'inherit'
    RewriteRule         ^/(perl/.*)$     http://127.0.0.1:8001/$1    [P,L]
    ProxyPassReverse    /  http://www.example.com/
</VirtualHost>

##### www.example.org
<VirtualHost 192.168.1.2:80>
    ServerName      www.example.org
    ServerAdmin     webmaster@example.org
    DocumentRoot    /home/httpd_docs/htdocs/www.example.org

    RewriteEngine       on
    RewriteOptions      'inherit'
    RewriteRule         ^/(perl/.*)$     http://127.0.0.1:8002/$1    [P,L]
    ProxyPassReverse    /  http://www.example.org/
</VirtualHost>

The two virtual hosts' setups differ in the DocumentRoot and ProxyPassReversesettings and in the backend ports to which they rewrite.

12.10.5. Backend Server Configuration

The backend server listens on the loopback (localhost) interface:

BindAddress           127.0.0.1

In this context, the following directive does not specify a listening port:

Port                  80

Rather, it indicates which port the server should advertise when issuing a redirect.

The following global mod_perl settings are shared by all virtual hosts:

##### mod_perl settings
PerlRequire                   /home/httpd/perl/startup.pl
PerlFixupHandler              Apache::SizeLimit
PerlPostReadRequestHandler    Book::ProxyRemoteAddr
PerlSetupEnv                  Off

As explained earlier, we use the Book::ProxyRemoteAddr handler to get the real remote IP addresses from the proxy.

We can then proceed to configure the virtual hosts themselves:

##### www.example.com
Listen 8001
<VirtualHost 127.0.0.1:8001>

The Listen directive specifies the port to listen on. A connection to that port will be matched by this <VirtualHost> container.

The remaining configuration is straightforward:

ServerName  www.example.com
ServerAdmin webmaster@example.com

<Location /perl>
    SetHandler perl-script
    PerlHandler Apache::Registry
    Options +ExecCGI
</Location>

<Location /perl-status>
    SetHandler perl-script
    PerlHandler Apache::Status
</Location>

  </VirtualHost>

We configure the second virtual host in a similar way:

##### www.example.org
Listen 8002
<VirtualHost 127.0.0.1:8002>
    ServerName  www.example.org
    ServerAdmin webmaster@example.org

    <Location /perl>
        SetHandler perl-script
        PerlHandler Apache::Registry
        Options +ExecCGI
    </Location>

</VirtualHost>

You may need to specify the DocumentRootsetting in each virtual host if there is any need for it.