Sun Java System Communications Services 6 2005Q4 Deployment Planning Guide

Directory Server and High Availability

From the Communications Services standpoint, the most important factor in planning your directory service is availability. As an infrastructure service, the directory must provide as near-continuous service as possible to the higher-level applications for authorization, access, email routing, and so forth.

A key feature of Directory Server that provides for high availability is replication. Replication is the mechanism that automatically copies directory data from one Directory Server to another. Replication enables you to provide a highly available directory service, and to geographically distribute your data. In practical terms, replication brings the following benefits:

The following table shows how you can design your directory for availability.

Table 6–1 Designing Directory Server for High Availability



Single-master replication 

A server acting as a supplier copies a master replica directly to one or more consumer servers. In this configuration, all directory modifications are made to the master replica stored on the supplier, and the consumers contain read-only copies of the data. 

Two-way, multi-master replication 

In a multimaster environment between two suppliers that share responsibility for the same data, you create two replication agreements. Supplier A and Supplier B each hold a master replica of the same data and there are two replication agreements governing the replication flow of this multimaster configuration. 

Four-way multi-master 

Provides a pair of Directory Server masters, usually in two separate data centers. This configuration uses four-way MultiMaster Replication (MMR) for replication. Thanks to its four-way master failover configuration, this fully-connected topology provides a highly-available solution that guarantees data integrity. When used with hubs in the replication topology, load distribution is facilitated, and the four consumers in each data center allow this topology to scale for read (lookup) operations. 

Sun Cluster Agent for Directory Server

Using Sun Cluster software provides the highest level of availability for your directory implementation. In the case of failure of an active Directory Server node, Sun Cluster provides for transparent failover of services to a backup node. However, the administrative (and hardware) costs of installing, configuring, and maintaining a cluster are typically higher than the Directory Server replication methods. 

See the Sun Java System Directory Server 5 2005Q1 Deployment Plannning Guide for more information.