Clustering basics
All the servers in an HCL Domino cluster continually communicate with each other to keep updated on the status of each server and to keep database replicas synchronized.
How failover works
An HCL Domino server cluster's ability to redirect requests from one server to another is called failover. When a user tries to access a database on a server that is unavailable or in heavy use, Domino directs the user to a replica of the database on another server in the cluster.
How workload balancing works
By distributing databases throughout theHCL Domino server cluster, you balance the workload in the cluster so that no server is overloaded.
The cluster components
Several components -- the Cluster Manager, Cluster Database Directory, Cluster Database Directory Manager, Cluster Administrator, and Cluster Replicator -- work together to make clustering function correctly. In addition, the Internet Cluster Manager clusters HCL Domino servers that run Internet protocols.
How replication works in a cluster
Cluster replication is event-driven, rather than schedule-driven. When the Cluster Replicator learns of a change to a database, it immediately pushes that change to other replicas in the cluster. If there is a backlog of replication events, the Cluster Replicator stores these in memory until it can push them to the other cluster servers. If a change to the same database occurs before a previous change has been sent, the Cluster Replicator pools these changes and sends them together to save processing time.
Mail failover in a Domino server cluster
Depending on how your HCL Domino server cluster is configured, mail fails over in one of several ways.
How calendars work in a cluster
HCL Domino supports clustering of calendars and the Free Time database. When clustered, the scheduling system works a little differently behind the scenes than when it is not clustered. However, these differences are not noticeable to users.
How operating system clusters work
The method of clustering that HCL Domino uses is called "application clustering." Domino, which is an application, monitors the cluster and determines when failover and workload balancing should occur, based on parameters that you set. Another form of clustering is "operating system clustering." In this form of clustering, the operating system monitors the cluster and determines when failover should occur. When failover occurs, the server (called a node) to which you fail over takes over the resources of the failed node, accesses the storage space the failed node was accessing, and runs the applications the failed node was running.