The Lightweight Directory Access Protocol (LDAP) is a set of protocols designed to access and maintain information directories. LDAP can be used for numerous purposes, such as user and group management, system configuration management, or address management. This chapter provides a basic understanding of how OpenLDAP works and how to manage LDAP data with YaST. While there are several implementations of the LDAP protocol, this chapter focuses entirely on the OpenLDAP implementation.
It is crucial within a networked environment to keep important information structured and quickly available. This can be done with a directory service that, like the common yellow pages, keeps information available in a well-structured, quickly searchable form.
In the ideal case, a central server keeps the data in a directory and distributes it to all clients using a certain protocol. The data is structured in a way that allows a wide range of applications to access it. That way, it is not necessary for every single calendar tool and e-mail client to keep its own database—a central repository can be accessed instead. This notably reduces the administration effort for the information. The use of an open and standardized protocol like LDAP ensures that as many different client applications as possible can access such information.
A directory in this context is a type of database optimized for quick and effective reading and searching:
To make numerous concurrent reading accesses possible, the number of updates is usually very low compared to the number of read accesses and write access is often limited to a few users with administrative priviledges. Conventional databases are optimized for accepting the largest possible data volume in a short time.
When static data is administered, updates of the existing data sets are very rare. When working with dynamic data, especially when data sets like bank accounts or accounting are concerned, the consistency of the data is of primary importance. If an amount should be subtracted from one place to be added to another, both operations must happen concurrently, within one transaction, to ensure balance over the data stock. Traditional relational databases usually have a very strong focus on data consistancy, such as referential integrity support of transactions. Opposed to that short-term inconsitancies are usually acceptable in LDAP directories. LDAP directories often do not have such strong consistancy requirements as relational databases.
The design of a directory service like LDAP is not laid out to support complex update or query mechanisms. All applications accessing this service should gain access quickly and easily.