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.
Once the cluster administrative domain is created,
it can be managed with CL commands or the Cluster Resource Services
graphical interface in IBM Navigator
for i. Monitored resources
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 can only be added to the cluster administrative domain if all
nodes in the domain are active and participating in the group. MREs
cannot be added in the cluster administrative domain if the domain
has status of Partitioned.
To use the Cluster Resource Services graphical interface
or the Display
CRG Information (DSPCRGINF) command, you must have
the IBM PowerHA for i licensed
program installed.Cluster APIs to
determine the status of a cluster administrative domain. 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) 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 command will help you figure out which MRE(s) are not
consistent and on what systems.