Virtual Services Howto: Virtual Web

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Apache has their own support for virtual domains. This is the only program I recommend using the internal virtual domain mechanism. When you run something through inetd there is a cost, the program has to start up each time you run it. This results in slower response time, which is perfectly fine for most services but is completely unacceptable for web service. Apache also has a mechanism for stopping connections when too many come in, which can be critical for even medium volume sites.

Simply stated, virtualizing Apache with virtuald is a really bad idea. The whole point of virtuald is to fill the gap created when services DO NOT have their own internal mechanism to do the job. Virtuald is not meant to replace good code that already completes the task at hand.

The above not withstanding here is how to do it for those who are foolhardy enough to do so.

Inetd

Edit /etc/inetd.conf

vi /etc/inetd.conf # Add this line
www stream tcp nowait www /usr/local/bin/virtuald \
        virtuald /virtual/conf.www httpd -f /var/www/conf/httpd.conf

Httpd.conf

Edit /var/www/conf/httpd.conf

vi /var/www/conf/httpd.conf # Or wherever you put the Apache config files
It should say:
ServerType standalone

Replace it with:
ServerType inetd

Configuration

Then configure each instance of the Apache server like you would normally for single domain use.

Httpd.init

An httpd.init file is not needed since the server is run through inetd.

8.2 Running With Apache VirtualHost

Apache has three configuration files access.conf , httpd.conf , and srm.conf . Newer versions of Apache have made the three configuration files unnecessary. However, I find that breaking up the configuration into three sections makes it easier to manage so I will be keeping with that style in this HOWTO document.

Access.conf

This configuration file is used to control the accessibility of directories in the web directory structure. Here is a sample configuration file that shows how to have different options for each domain.

# /var/www/conf/access.conf: Global access configuration

# Options are inherited from the parent directory
# Set the main directory with default options
<Directory />
AllowOverride None
Options Indexes
</Directory>

# Give one domain a passwd protected directory
<Directory /virtual/domain1.com/var/www/html/priv>
AuthUserFile /var/www/passwd/domain1.com-priv
AuthGroupFile /var/www/passwd/domain1.com-priv-g
AuthName PRIVSECTION
AuthType Basic
<Limit GET PUT POST>
require valid-user
</Limit>
</Directory>

# Give another domain Server Side Includes
<Directory /virtual/domain2.com/var/www/html>
Options IncludesNOEXEC
</Directory>

Httpd.conf

This configuration file is used to control the main options for the Apache server. Here is a sample configuration file that shows how to have different options for each domain.

# /var/www/conf/httpd.conf: Main server configuration file

# Begin: main conf section

# Needed since not using inetd
ServerType standalone

# Port to run on
Port 80

# Log clients with names vs IP addresses
HostnameLookups on

# User to run server as
User www
Group www

# Where server config, error and log files are
ServerRoot /var/www

# Process Id of server in this file
PidFile /var/run/httpd.pid

# Internal server process info
ScoreBoardFile /var/www/logs/apache_status

# Timeout and KeepAlive options
Timeout 400
KeepAlive 5
KeepAliveTimeout 15

# Number of servers to run
MinSpareServers 5
MaxSpareServers 10
StartServers 5
MaxClients 150
MaxRequestsPerChild 30

# End: main conf section

# Begin: virtual host section

# Tell server to accept requests for ip:port
# I have one for each IP needed so you can explicitly ignore certain domains
Listen 10.10.10.129:80
Listen 10.10.10.130:80

# VirtualHost directive allows you to specify another virtual
# domain on your server.  Most Apache options can be specified
# within this section.
<VirtualHost www.domain1.com>

# Mail to this address on errors
ServerAdmin [email protected]

# Where documents are kept in the virtual domain
DocumentRoot /virtual/domain1.com/var/www/html

# Name of the server
ServerName www.domain1.com

# Log files Relative to ServerRoot option
ErrorLog logs/domain1.com-error_log
TransferLog logs/domain1.com-access_log
RefererLog logs/domain1.com-referer_log
AgentLog logs/domain1.com-agent_log

# Use CGI scripts in this domain
ScriptAlias /cgi-bin/ /var/www/cgi-bin/domain1.com/
AddHandler cgi-script .cgi
AddHandler cgi-script .pl
</VirtualHost>

<VirtualHost www.domain2.com>

# Mail to this address on errors
ServerAdmin [email protected]

# Where documents are kept in the virtual domain
DocumentRoot /virtual/domain2.com/var/www/html

# Name of the server
ServerName www.domain2.com

# Log files Relative to ServerRoot option
ErrorLog logs/domain2.com-error_log
TransferLog logs/domain2.com-access_log
RefererLog logs/domain2.com-referer_log
AgentLog logs/domain2.com-agent_log

# No CGI's for this host
</VirtualHost>
# End: virtual host section

Srm.conf

This configuration file is used to control how requests are serviced and how results are formatted. You do not have to edit anything here for the virtual domains. The sample config file from Apache should work.

Httpd.init

Nothing special has to be done to the httpd.init file. Use a standard one that comes with the Apache configuration.

8.3 File Descriptor Overflow

Warning

This only applies to the standalone style Apache server. A server run through inetd does not interact with the other domains so it has the whole file descriptor table.

Every log file that the Apache server opens is another file descriptor for the process. There is a limit of 256 file descriptors per process in Linux. Since you have multiple domains you are using a lot more file descriptors. If you have too many domains running off of one Apache web server process you can overflow this table. This would mean that certain logs would not work and CGI's would fail.

Multiple Apache Servers

If you assume five file descriptors per domain you can have 50 domains running on your Apache server without any problems. However, if you find your server having problems like this you could create /var/www1 with an Apache server in charge of domain1 - domain25 and /var/www2 with an Apache server in charge of domain26 - domain50 and so on. This would give each server their own configuration, error, and log directory. Each server should be configured separately with their own Listen and VirtualHost directives. Do not forget to run multiple servers in your httpd.init file.

8.4 Sharing Servers With One IP

Saving IPs

The HTTP (HyperText Transfer Protocol) version 1.1 added a feature that communicates the name of the server to the client. This means that the client does not need to look up the server from its IP address. Therefore, two virtual servers could have the same IP address and be different web sites. The Apache configuration is the same as above except that you do not have to put in a different Listen directive since the two domains will have the same IP.

Drawback

The only problem is that virtuald uses IP addresses to distinguish between domains. In its current form virtuald would not be able to chroot to different spool directories for each domain. Therefore, mail would only be able to respond as one IP and there would no longer be a unique spool directory for each domain. All the web sharing IP clients would have to share that IPs spool directory. That would mean duplicate usernames would be an issue again. However, that is the price you pay for sharing IPs.

8.5 More Information

This HOWTO only shows how to implement virtual support on the Apache web server. Most web servers use a similar interface. For more information on virtual web hosting consult the WWW HOWTO, the documentation for Apache at Apache's Site, or the documentation at ApacheWeek.