Cluster administrative domain
A cluster administrative domain provides a mechanism of maintaining a consistent operational environment across cluster nodes within an IBM® i high availability environment. A cluster administrative domain ensures that highly available applications and data behave as expected when switched to or failed over to backup nodes.
There are often configuration parameters or data associated with applications and application data which are known collectively as the operational environment for the application. Examples of this type of data include user profiles used for accessing the application or its data, or system environment variables that control the behavior of the application. With a high availability environment, the operational environment needs to be the same on every system where the application can run, or where the application data resides. When a change is made to one or more configuration parameters or data on one system, the same change needs to be made on all systems. A cluster administrative domain lets you identify resources that need to be maintained consistently across the systems in an IBM i high availability environment. The cluster administrative domain then monitors for changes to these resources and synchronizes any changes across the active domain.
When a cluster administrative domain is created, the system creates a peer CRG with the same name. The nodes that make up the cluster administrative domain are defined by the CRGs recovery domain. Node membership of the cluster administrative domain can be modified by adding and removing nodes from the recovery domain using Add Cluster Admin Domain Node Entry (ADDCADNODE) and Remove Cluster Admin Domain Node Entry (RMVCADNODE) or by using the Work Cluster (WRKCLU) command. Each cluster node can be defined in only one cluster administrative domain within the cluster.
A monitored resource is a system resource that is managed by a cluster administrative domain. Changes made to a monitored resource are synchronized across nodes in the cluster administrative domain and applied to the resource on each active node. Monitored resources can be system objects such as user profiles or job descriptions. A monitored resource can also be a system resource not represented by a system object, such as a single system value or a system environment variable. These monitored resources are represented in the cluster administrative domain as monitored resource entries (MREs).
Cluster administrative domain supports monitored resources with simple attributes and compound attributes. A compound attribute differs from a simple attribute in that it contains zero or more values, while a simple attribute contains a single value. Subsystem Descriptions (*SBSD) and Network Server Descriptions (*NWSD) are examples of monitored resources that contain compound attributes.
In order for MREs to be added, the resource must exist on the node from which the MREs are added. If the resource does not exist on every node in the administrative domain, the monitored resource is created. If a node is later added to the cluster administrative domain, the monitored resource is created. MREs cannot be added in the cluster administrative domain if the domain has status of Partitioned.
When an MRE is added to the cluster administrative domain, changes made to the resource on any active node in the cluster administrative domain are propagated to all nodes in the active domain. When a node within a cluster administrative domain is inactive, the synchronization option controls the way changes are propagated throughout the cluster. When the synchronization option is set to Active Domain, any changes made to the resource on the inactive node are discarded when the node rejoins the cluster. When the synchronization option is set to Last Change, changes made to the resource on the inactive node are only discarded if there was a more recent change to the resource propagated in the cluster administrative domain. When the cluster administrative domain is deleted, all monitored resource entries that are defined in the cluster administrative domain are removed; however, the actual resource is not removed from any node in the active domain.
To help you manage the administrative domain with many MREs, the Print Admin Domain MRE (PRTCADMRE) or Work with Monitored Resources (WRKCADMRE) command can be used. Information that can be printed or directed to a database output file and can be used to write additional tools, perform queries, or manage the monitored resource in the administrative domain. If your monitored resources ever have a global status of inconsistent, the PRTCADMRE or WRKCADMRE command helps you figure out which MRE(s) are not consistent and on what systems.