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The multihost shared disk is used in the above configuration for storing LDAP data. In addition, most LDAP vendors support a master and replica architecture that makes it possible for you to configure a HA LDAP without shared disks. Install clustering software on both nodes, and configure LDAP to use local data.
The primary node is configured as the LDAP master, and the backup node is configured as the LDAP replica, as shown in Figure 15-12. Any LDAP change requests that go to the replica server are referred to the master server because the replica server cannot change data. The master server sends all changes to the replica server to synchronize its data.
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Replication is not part of the LDAP standard. Therefore, the master-replica function is implemented vendor specific and can differ from product to product. Refer to your LDAP administration manuals for information about how to use and configure this option. |
Figure 15-12 Clustered master-replica LDAP with individual disks
When the primary server (master) is down due to some network, hardware, or software reason, the LDAP service is moved to the backup server under the control of the clustering software. The replica server is promoted temporarily to the master server and continues to service LDAP requests, as shown in Figure 15-13.
Figure 15-13 Clustered master-replica LDAP with individual disks after failover
When the primary node is up again, you can move the LDAP service back to the primary node. You should not configure automatic fallback, because by doing so, you will lose all updates. We need to export the latest data from the backup server manually and import it to the primary server before you start the primary LDAP server again. It takes time to synchronize the data in the master server in this share-nothing configuration. In the shared disks LDAP configuration, because you use the same data in the shared disks, you do not need to synchronize the data between two servers. However, it is easier to configure the cluster without shared disks.
