At work, we had set up some wildcard virtual hosts in Apache config, and that got us by for quite some time.  But the time came when we needed finer-grained control of where to send incoming requests for different domains.  I needed to store my virtual hosts in a Mysql database, mapping domains to project directories.

I’ll spare you the problems I ran into and overcame, and just list the steps to get this done.  These instructions are based on a 64-bit, RHEL 5 server running the pre-packaged Apache server.  So if you follow these instructions on a different setup, of course, filenames, directories, versions, etc. may differ.

Install mod_vhost_dbd

Download dbd-modules from Google Code.  This is a great piece of code in the form of an Apache module that uses mod_dbd and a DBD Mysql (or other database) driver to fetch the DocumentRoot for a given domain from a database.

% wget http://dbd-modules.googlecode.com/files/dbd-modules-1.0.5.zip

Unzip the archive in a directory. As indicated on the website, build and install the module.

% apxs -c mod_vhost_dbd.c
% apxs -i mod_vhost_dbd.la

This places mod_vhost_dbd.so in /usr/lib64/httpd/modules.  Enable both this module and mod_dbd by adding two lines to httpd.conf, or equivalently creating a new include file in /etc/httpd/conf.d containing these lines.

LoadModule dbd_module modules/mod_dbd.so
LoadModule vhost_dbd_module modules/mod_vhost_dbd.so

In true unit fashion, now might be a good time to restart Apache, just so you can be sure everything is working up to this point.

% service httpd restart

Install Mysql DBD Driver to APR

Unfortunately, on my system, the Mysql DBD driver was nowhere to be found.  I had to rebuild Apache Portable Runtime (APR) utils with the Mysql driver enabled.

Download apr and apr-util from Apache.  Note these are not the latest versions, but the versions that matched the packages in worked for RHEL 5.

% wget http://archive.apache.org/dist/apr-1.2.8.tar.bz2
% wget http://archive.apache.org/dist/apr-util-1.2.8.tar.bz2

Unpack and untar these archives in the same parent directory.

Build and install APR.  Now, I do not think this is absolutely necessary, but it seems like a good idea to keep the versions in sync.

% ./configure --prefix=/usr
% make
% make install

Build and install apr-util.  Due to licensing issues, apr-util does not actually contain the Mysql DBD driver until apr-util-1.2.12.  Prior to that version, it must be downloaded separately, and the configure script rebuilt.

% wget http://apache.webthing.com/svn/apache/apr/apr_dbd_mysql.c
% ./buildconf --with-apr=../apr-1.2.7

Now for the three commands every Linux admin loves.

% ./configure --prefix=/usr --with-apr=/usr --libdir=/usr/lib64 --with-expat=builtin --with-ldap-include=/usr/include --with-ldap-lib=/usr/lib64 --with-ldap=ldap --with-mysql
% make
% make install

The first time I tried this, Apache could not find any LDAP-related modules.  Adding those configure switches seemed to do the trick.  Restart Apache.

% service httpd restart

Apache should now be able to query a Mysql database to get the DocumentRoot for a domain.  My VirtualHost block looked something like this.

<VirtualHost *:80>
    ServerName *.example.com
    DocumentRoot "/path/to/default/document/root"
 
    DBDriver mysql
    DBDParams host=localhost,user=root,pass=secret,dbname=vhosts
 
    DBDocRoot "SELECT path FROM vhosts WHERE host = %s"  HOSTNAME
</VirtualHost>

For more details and instructions on mod_vhost_dbd configuration directives, read the project wiki.