About Domino clustering components

Several components work together to control a Domino cluster. These components include the Cluster Manager, the Cluster Database Directory, the Cluster Database Directory Manager, and the Cluster Replicator.

The Cluster Manager runs on each server in a Domino cluster and monitors the state of the other servers in the Domino cluster.

The Cluster Manager performs the following tasks:

Determines which servers belong to the Domino cluster
Monitors for server availability and workload
Fails over database requests due to unavailability of a clustered Domino server
Performs workload balancing

The Cluster Database Directory (CLDBDIR.NSF) is replicated on every server in a Domino cluster. The Cluster Database Directory contains information for each database on each server in the Domino cluster. This information includes file name, server, replica ID, cluster replication status, and out of service information. The different cluster components use this information to perform their tasks.

The Cluster Database Directory Manager (CLDBDIR) task on each server manages the Cluster Database Directory and keeps it up to date. The Cluster Database Directory Manager also monitors the status of each database to determine if they are out of service or not yet deleted.

The Cluster Replicator (CLREPL) task constantly synchronizes the database replicas in a Domino cluster. Changes to the database are pushed immediately to the other replicas in the cluster. This event-drive replication ensures that each time a database is accessed that it contains the most up-to-date data. The Cluster Replicator task pushes changes only to those servers in a Domino cluster. The traditional scheduled replication is used to replicate changes to and from servers outside a Domino cluster.

Because Domino stores replication events in memory only, both the source server and destination server must be available for the replication to complete successfully. If a destination server is not available, the replication events are stored on the source server until the destination server becomes available. If the source server shuts down before the replication completes, the replication events in memory are lost. To prevent this loss, configure immediate replication with all members of the Domino cluster whenever a Domino cluster server is restarted. Perform scheduled replications between Domino clustered servers on a regular basis to help maintain database consistency for all members of the Domino cluster.