Use this task to continue the configuration of a One of N messaging engine policy.
A One of N policy can be used to run a
messaging engine in
a cluster to provide a failover capability. One cluster server runs the
messaging engine whilst the remaining
cluster servers act as standby servers, ready to run the
messaging engine should
it no longer be able to run in its current server. This type of policy can
also manage a
messaging engine running
in a server bus member, however this is equivalent to a cluster with only
one server (in other words the value of N is 1), and does not provide failover.
- If required, define one or more preferred
servers:
- Click coregroup_namepolicyname.
- Select the servers you require from the left hand pane and add
them to the right hand pane.
- Adjust the order of your list as required. If you
specify multiple preferred servers the order in which they are specified is
important. There is an implicit stronger preference for a server that appears
earlier in the list.
- Click OK.
Defining preferred servers specifies that the messaging engine should
run in one of the cluster servers that is preferred over the others. This
can be used to help spread workload across the cluster, or may be necessary
if one server has more resources available to it or typically performs less
work than the others.
- If required, restrict the messaging engine to
run only on preferred servers, by selecting the Preferred servers
only check box. The messaging engine will
now be incapable of running on a server that is not in the preferred servers
list.
- If required, specify that the messaging engine should
automatically fail back to a preferred server, by selecting the Fail
back check box. When the messaging engine is
not running on one of its preferred servers, it will now automatically move
back to one of its preferred servers if one becomes available. In addition,
if the messaging engine is running
on a preferred server, and a server which appears earlier in the preferred
servers list becomes available, the messaging engine will
be automatically moved to that server.
- Ensure that the messaging engine can
always reach its data store. If the messaging engine is
configured to be able to failover then its data store must be accessible from
any server in the cluster on which the messaging engine may
run. The set of possible servers depends on whether you have configured preferred
servers and whether you have set the Preferred servers only option.
For example, suppose you have a cluster of three servers, server1, server2
and server3, containing a messaging engine using
a policy that allows it to fail over to any of the servers in the cluster.
The data store for the messaging engine must
be accessible from all three servers. If however you configure the messaging engine's
policy with preferred servers server1 and server2, and set the Preferred
servers only option, then only server1 and server2 would need
access to the data store for that messaging engine.
- If required, alter the isAlive health
monitoring interval. This determines the frequency with which the HAManager checks that a messaging engine is
running properly. The default is 120 seconds.
- Click OK.
- Save your changes to the master configuration.