With more and more companies investigating capabilities such as identity management, SSO (single sign-on), and automated provisioning, directory services are fast becoming a vital component of network infrastructures. So far, however, no open source project has gained as much traction in this area as Apache enjoys in the Web server market.
The chief contender has long been OpenLDAP, a project that provides a reliable, scalable, stable LDAP directory server, a replication server, and some basic tools. The OpenLDAP Foundation maintains the code under a custom license and has ported it to a variety of platforms, including AIX, FreeBSD, Linux, Mac OS X, and Windows. OpenLDAP is mature and it works, but it can be difficult to configure, especially when it comes to writing ACLs (access control lists). It's also primarily a workhorse server, lacking some of the "frosting" of commercial LDAP directories from the likes of Microsoft, Novell, and Sun Microsystems.
Novell has made open source a core part of its strategy, but unfortunately for network administrators, eDirectory remains part of its commercial software portfolio -- a fact that gave rival Linux vendor Red Hat the opportunity to step up to the plate with an open source offering of its own. Based on the product formerly known as Netscape Directory, which Red Hat acquired from Netscape in 2004, RHDS (Red Hat Directory Server) is available for Windows, Solaris (Sparc processors), and HP-UX (PA-RISC processors). A mature product with considerable history, RHDS offers advanced features such as replication -- including fractional replication, special features for large databases, and replication over WAN links -- and synchronization with Microsoft Active Directory and Windows NT4 Server.
Currently, RHDS is available to customers only under Red Hat's subscription-based support model. The company, however, has already begun the process of open sourcing the software as a GPL (General Public License)-licensed project called Fedora Directory Server. As of this writing, only the core LDAP server itself and some command-line tools are available as open source, but work is in progress on other server modules, as well as the management console and administration server components.
Many observers believe that, in the long run, the Fedora project will probably prove to be a superior choice to OpenLDAP for those looking for an open source directory server. But with OpenLDAP well entrenched as the de facto standard for budget directory deployments, it's unlikely to disappear anytime soon. Either package is a solid choice for basic directory functionality, even for large databases.