Virtual Host examples for common setups

Base configuration

IP-based vhosts only
Name-based vhosts only
Mixed name-/IP-based vhosts
Port-based vhosts

Additional features

Using _default_ vhosts
Migrating a named-based vhost to an IP-based vhost
Using the ServerPath directive

IP-based vhosts only

Setup 1: The server machine has two IP addresses (111.22.33.44 and 111.22.33.55) which resolve to the names server.domain.tld and www.otherdomain.tld respectively. The hostname www.domain.tld is an alias (CNAME) for server.domain.tld and will represent the main server.
Server configuration:
```
    ...
    Port 80
    DocumentRoot /www/domain
    ServerName www.domain.tld

    <VirtualHost 111.22.33.55>
    DocumentRoot /www/otherdomain
    ServerName www.otherdomain.tld
    ...
    </VirtualHost>
    
```
www.otherdomain.tld can only be reached through the address 111.22.33.55, while www.domain.tld can only be reached through 111.22.33.44 (which represents our main server).

Setup 2: Same as setup 1, but we don't want to have a dedicated main server.

Server configuration:

    ...
    Port 80
    ServerName server.domain.tld
    
    <VirtualHost 111.22.33.44>
    DocumentRoot /www/domain
    ServerName www.domain.tld
    ...
    </VirtualHost>

    <VirtualHost 111.22.33.55>
    DocumentRoot /www/otherdomain
    ServerName www.otherdomain.tld
    ...
    </VirtualHost>
    
The main server can never catch a request, because all IP addresses of our machine are in use for IP-based virtual hosts (only localhost requests can hit the main server).

Setup 3: The server machine has two IP addresses (111.22.33.44 and 111.22.33.55) which resolve to the names server.domain.tld and www-cache.domain.tld respectively. The hostname www.domain.tld is an alias (CNAME) for server.domain.tld and will represent the main server. www-cache.domain.tld will become our proxy-cache listening on port 8080, while the web server itself uses the default port 80.
Server configuration:
```
    ...
    Port 80
    Listen 111.22.33.44:80
    Listen 111.22.33.55:8080
    ServerName server.domain.tld
    
    <VirtualHost 111.22.33.44:80>
    DocumentRoot /www/domain
    ServerName www.domain.tld
    ...
    </VirtualHost>

    <VirtualHost 111.22.33.55:8080>
    ServerName www-cache.domain.tld
    ...
      <Directory proxy:>
      order deny,allow
      deny from all
      allow from 111.22.33
      </Directory>
    </VirtualHost>
    
```
The main server can never catch a request, because all IP addresses (apart from localhost) of our machine are in use for IP-based virtual hosts. The web server can only be reached on the first address through port 80 and the proxy only on the second address through port 8080.

Name-based vhosts only

Setup 1: The server machine has one IP address (111.22.33.44) which resolves to the name server.domain.tld. There are two aliases (CNAMEs) www.domain.tld and www.sub.domain.tld for the address 111.22.33.44.
Server configuration:
```
    ...
    Port 80
    ServerName server.domain.tld

    NameVirtualHost 111.22.33.44 

    <VirtualHost 111.22.33.44>
    DocumentRoot /www/domain
    ServerName www.domain.tld
    ...
    </VirtualHost>
    
    <VirtualHost 111.22.33.44>
    DocumentRoot /www/subdomain
    ServerName www.sub.domain.tld
    ...
    </VirtualHost> 
    
```
Apart from localhost there are no unspecified addresses/ports, therefore the main server only serves localhost requests. Due to the fact that www.domain.tld has the highest priority it can be seen as the default or primary server.
Setup 2: The server machine has two IP addresses (111.22.33.44 and 111.22.33.55) which resolve to the names server1.domain.tld and server2.domain.tld respectively. The alias www.domain.tld should be used for the main server which should also catch any unspecified addresses. We want to use a virtual host for the alias www.otherdomain.tld and one virtual host should catch any request to hostnames of the form *.sub.domain.tld with www.sub.domain.tld as its server name. The address 111.22.33.55 should be used for the virtual hosts.
Server configuration:
```
    ...
    Port 80
    ServerName www.domain.tld
    DocumentRoot /www/domain

    NameVirtualHost 111.22.33.55

    <VirtualHost 111.22.33.55>
    DocumentRoot /www/otherdomain
    ServerName www.otherdomain.tld
    ...
    </VirtualHost>
   
    <VirtualHost 111.22.33.55>
    DocumentRoot /www/subdomain
    ServerName www.sub.domain.tld
    ServerAlias *.sub.domain.tld
    ...
    </VirtualHost> 
    
```
Any request to an address other than 111.22.33.55 will be served from the main server. A request to 111.22.33.55 with an unknown or no Host: header will be served from www.otherdomain.tld.

Setup: The server machine has three IP addresses (111.22.33.44, 111.22.33.55 and 111.22.33.66) which resolve to the names server.domain.tld, www.otherdomain1.tld and www.otherdomain2.tld respectively. The address 111.22.33.44 should we used for a couple of name-based vhosts and the other addresses for IP-based vhosts.

Server configuration:

    ...
    Port 80
    ServerName server.domain.tld

    NameVirtualHost 111.22.33.44

    <VirtualHost 111.22.33.44>
    DocumentRoot /www/domain
    ServerName www.domain.tld
    ...
    </VirtualHost>
   
    <VirtualHost 111.22.33.44>
    DocumentRoot /www/subdomain1
    ServerName www.sub1.domain.tld
    ...
    </VirtualHost> 
    
    <VirtualHost 111.22.33.44>
    DocumentRoot /www/subdomain2
    ServerName www.sub2.domain.tld
    ...
    </VirtualHost> 
 
    <VirtualHost 111.22.33.55>
    DocumentRoot /www/otherdomain1
    ServerName www.otherdomain1.tld
    ...
    </VirtualHost> 
    
    <VirtualHost 111.22.33.66>
    DocumentRoot /www/otherdomain2
    ServerName www.otherdomain2.tld
    ...
    </VirtualHost>

Port-based vhosts

Setup: The server machine has one IP address (111.22.33.44) which resolves to the name www.domain.tld. If we don't have the option to get another address or alias for our server we can use port-based vhosts if we need a virtual host with a different configuration.
Server configuration:
```
    ...
    Listen 80
    Listen 8080
    ServerName www.domain.tld
    DocumentRoot /www/domain

    <VirtualHost 111.22.33.44:8080>
    DocumentRoot /www/domain2
    ...
    </VirtualHost>
    
```
A request to www.domain.tld on port 80 is served from the main server and a request to port 8080 is served from the virtual host.

Using `_default_` vhosts

Setup 1: Catching every request to any unspecified IP address and port, i.e., an address/port combination that is not used for any other virtual host.
Server configuration:
```
    ...
    <VirtualHost _default_:*>
    DocumentRoot /www/default
    ...
    </VirtualHost>
    
```
Using such a default vhost with a wildcard port effectively prevents any request going to the main server.
A default vhost never serves a request that was sent to an address/port that is used for name-based vhosts. If the request contained an unknown or no Host: header it is always served from the primary name-based vhost (the vhost for that address/port appearing first in the configuration file).
You can use AliasMatch or RewriteRule to rewrite any request to a single information page (or script).
Setup 2: Same as setup 1, but the server listens on several ports and we want to use a second _default_ vhost for port 80.
Server configuration:
```
    ...
    <VirtualHost _default_:80>
    DocumentRoot /www/default80
    ...
    </VirtualHost>
    
    <VirtualHost _default_:*>
    DocumentRoot /www/default
    ...
    </VirtualHost>    
    
```
The default vhost for port 80 (which must appear before any default vhost with a wildcard port) catches all requests that were sent to an unspecified IP address. The main server is never used to serve a request.
Setup 3: We want to have a default vhost for port 80, but no other default vhosts.
Server configuration:
```
    ...
    <VirtualHost _default_:80>
    DocumentRoot /www/default
    ...
    </VirtualHost>
    
```
A request to an unspecified address on port 80 is served from the default vhost any other request to an unspecified address and port is served from the main server.

Migrating a name-based vhost to an IP-based vhost

Setup: The name-based vhost with the hostname www.otherdomain.tld (from our name-based example, setup 2) should get its own IP address. To avoid problems with name servers or proxies who cached the old IP address for the name-based vhost we want to provide both variants during a migration phase.
The solution is easy, because we can simply add the new IP address (111.22.33.66) to the VirtualHost directive.
Server configuration:
```
    ...
    Port 80
    ServerName www.domain.tld
    DocumentRoot /www/domain

    NameVirtualHost 111.22.33.55

    <VirtualHost 111.22.33.55 111.22.33.66>
    DocumentRoot /www/otherdomain
    ServerName www.otherdomain.tld
    ...
    </VirtualHost>
   
    <VirtualHost 111.22.33.55>
    DocumentRoot /www/subdomain
    ServerName www.sub.domain.tld
    ServerAlias *.sub.domain.tld
    ...
    </VirtualHost>
    
```
The vhost can now be accessed through the new address (as an IP-based vhost) and through the old address (as a name-based vhost).

Using the `ServerPath` directive

Setup: We have a server with two name-based vhosts. In order to match the correct virtual host a client must send the correct Host: header. Old HTTP/1.0 clients do not send such a header and Apache has no clue what vhost the client tried to reach (and serves the request from the primary vhost). To provide as much backward compatibility as possible we create a primary vhost which returns a single page containing links with an URL prefix to the name-based virtual hosts.
Server configuration:
```
    ...
    NameVirtualHost 111.22.33.44

    <VirtualHost 111.22.33.44>
    # primary vhost
    DocumentRoot /www/subdomain
    RewriteEngine On
    RewriteRule ^/.* /www/subdomain/index.html
    ...
    </VirtualHost>

    <VirtualHost 111.22.33.44>
    DocumentRoot /www/subdomain/sub1
    ServerName www.sub1.domain.tld
    ServerPath /sub1/
    RewriteEngine On
    RewriteRule ^(/sub1/.*) /www/subdomain$1 
    ...
    </VirtualHost>

    <VirtualHost 111.22.33.44>
    DocumentRoot /www/subdomain/sub2
    ServerName www.sub2.domain.tld
    ServerPath /sub2/
    RewriteEngine On
    RewriteRule ^(/sub2/.*) /www/subdomain$1 
    ...
    </VirtualHost>
    
```
Due to the ServerPath directive a request to the URL http://www.sub1.domain.tld/sub1/ is always served from the sub1-vhost.
A request to the URL http://www.sub1.domain.tld/ is only served from the sub1-vhost if the client sent a correct Host: header. If no Host: header is sent the client gets the information page from the primary host.
Please note that there is one oddity: A request to http://www.sub2.domain.tld/sub1/ is also served from the sub1-vhost if the client sent no Host: header.
The RewriteRule directives are used to make sure that a client which sent a correct Host: header can use both URL variants, i.e., with or without URL prefix.