Apache IP-based Virtual Host Support

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What is IP-based virtual hosting
System requirements
How to set up Apache
Setting up multiple daemons
Setting up a single daemon + with virtual hosts

What is IP-based virtual hosting

IP-based virtual hosting is a method to apply different directives +based on the IP address and port a request is received on. Most commonly, +this is used to serve different websites on different ports or interfaces.

+ +

In many cases, name-based +virtual hosts are more convenient, because they allow +many virtual hosts to share a single address/port. +See Name-based vs. IP-based +Virtual Hosts to help you decide.

System requirements

+ +

As the term IP-based indicates, the server + must have a different IP address/port combination for each IP-based + virtual host. This can be achieved by the machine + having several physical network connections, or by use of + virtual interfaces which are supported by most modern operating + systems (see system documentation for details, these are + frequently called "ip aliases", and the "ifconfig" command is + most commonly used to set them up), and/or using multiple + port numbers.

+ +

In the terminology of Apache HTTP Server, using a single IP address + but multiple TCP ports, is also IP-based virtual hosting.

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How to set up Apache

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There are two ways of configuring apache to support multiple + hosts. Either by running a separate httpd daemon for + each hostname, or by running a single daemon which supports all the + virtual hosts.

+ +

Use multiple daemons when:

+ +

There are security partitioning issues, such as company1 + does not want anyone at company2 to be able to read their + data except via the web. In this case you would need two + daemons, each running with different User, Group, Listen, and ServerRoot settings.
You can afford the memory and file descriptor + requirements of listening to every IP alias on the + machine. It's only possible to Listen to the "wildcard" + address, or to specific addresses. So if you have a need to + listen to a specific address for whatever reason, then you + will need to listen to all specific addresses. (Although one + httpd could listen to N-1 of the addresses, and another could + listen to the remaining address.)

+ +

Use a single daemon when:

+ +

Sharing of the httpd configuration between virtual hosts + is acceptable.
The machine services a large number of requests, and so + the performance loss in running separate daemons may be + significant.

+ +

Setting up multiple daemons

+ +

Create a separate httpd installation for each + virtual host. For each installation, use the Listen directive in the + configuration file to select which IP address (or virtual host) + that daemon services. e.g.

+ +

Listen 192.0.2.100:80

+ + +

It is recommended that you use an IP address instead of a + hostname (see DNS caveats).

+ +

Setting up a single daemon + with virtual hosts

+ +

For this case, a single httpd will service + requests for the main server and all the virtual hosts. The VirtualHost directive + in the configuration file is used to set the values of ServerAdmin, ServerName, DocumentRoot, ErrorLog and TransferLog + or CustomLog + configuration directives to different values for each virtual + host. e.g.

+ +

<VirtualHost 172.20.30.40:80>
+    ServerAdmin webmaster@www1.example.com
+    DocumentRoot "/www/vhosts/www1"
+    ServerName www1.example.com
+    ErrorLog "/www/logs/www1/error_log"
+    CustomLog "/www/logs/www1/access_log" combined
+</VirtualHost>
+
+<VirtualHost 172.20.30.50:80>
+    ServerAdmin webmaster@www2.example.org
+    DocumentRoot "/www/vhosts/www2"
+    ServerName www2.example.org
+    ErrorLog "/www/logs/www2/error_log"
+    CustomLog "/www/logs/www2/access_log" combined
+</VirtualHost>

+ + +

It is recommended that you use an IP address instead of a + hostname in the <VirtualHost> directive + (see DNS caveats).

+ +

Specific IP addresses or ports have precedence over their wildcard + equivalents, and any virtual host that matches has precedence over + the servers base configuration.

+ +

Almost any configuration directive can be + put in the VirtualHost directive, with the exception of + directives that control process creation and a few other + directives. To find out if a directive can be used in the + VirtualHost directive, check the Context using the + directive index.

+ +

SuexecUserGroup + may be used inside a + VirtualHost directive if the suEXEC + wrapper is used.

+ +

SECURITY: When specifying where to write log files, + be aware of some security risks which are present if anyone + other than the user that starts Apache has write access to the + directory where they are written. See the security tips document + for details.

+ +