Why Replicate?

When you replicate directory content, you increase the reliability and performance of your directory service. Let's examine these two benefits and how they are achieved.

By making the directory data available in more than one location, you improve the reliability of your directory service. If a single server fails, your directory clients and directory-enabled application programs can contact a different server for their directory service. Figure 11.1 illustrates how a client can use this redundancy to obtain service from a replica in the event of a server failure.

Figure 11.1. Increasing Reliability through Redundancy

When you replicate directory content, you also make your directory more resistant to outages due to network failures. In Figure 11.2, the directory-enabled application running on the LAN at the branch office can continue to function even if the network link between the branch office and company headquarters is down. Of course, the directory content on the replicated server may not be entirely up-to-date, but for the vast majority of applications slightly stale data is entirely acceptable. When the network connection between the offices is restored, Server B will once again be synchronized with Server A, eliminating any temporary differences.

Figure 11.2. Replicating to Minimize the Impact of a Network Failure

The situation in Figure 11.2 also exemplifies the benefit that replicas can be located close to the users and applications that need them. This arrangement improves performance because there are fewer network nodes between the LDAP clients and the directory data.

Thus, when you replicate directory content, you can also improve the performance of your directory. Your directory can be made to handle more directory client requests by distributing the load across more servers. Figure 11.3 illustrates the distribution of client load across multiple replicas.

Figure 11.3. Distributing Directory Client Load