This section describes the process of creating a Universal Messaging Cluster . Clusters allow a group of Universal Messaging Realm Servers to replicate resources between them, and to maintain the state for those objects across all realms within the cluster.

Creating a cluster of Universal Messaging realms ensures that applications which publish/subscribe to channels, or which push/pop events from queues, can connect to any of the realms and view the same state. If one of the realms in the cluster is unavailable, client applications can automatically reconnect to any of the other cluster realms and carry on from where they were.

Universal Messaging's clustering technology provides an unsurpassed level of reliability. Client applications can seamlessly switch between any cluster realm if any problems - such as network or hardware failures - occur with the realm to which they are connected. This also provides an exceptional ability to load balance clients between realm servers.

The Enterprise Manager's top level view shows a tree node labelled "Universal Messaging Enterprise" (see Enterprise Summary). One level below this is a tree node labelled "Clusters", which contains any known clusters.

If you use the Enterprise Manager to connect to a realm which is a member of an existing cluster, then the cluster will automatically be displayed under the above-mentioned "Clusters" tree node. When a cluster node is found, the Enterprise Manager will also automatically connect to all of the cluster member realms (if not already connected by default as a result of having loaded realm connection information in a custom Enterprise Manager Connection Profile (see Connecting to Multiple Realms).

Firstly, before a cluster can be created, the Enterprise Manager need to connect to those realms (see Connecting to Multiple Realms) that will form the cluster. If any realms cannot be connected to, or you receive a 'Security Alert' message when you click on the realm node, you may want to check that the realm is running, and check the permissions (see Realm Entitlements) on the realm. If the realms you are connecting to are running on different machines, you need to ensure that all realm machines are given full permissions to connect to the other realms in the cluster. Each realm communicates with the other cluster realms via its own connection. The subject of each connection is as follows:

For example, in the following example, there are 3 realms that will form part of a cluster, each realm subject needs to exists in the other realms ACLs, for example, the following realm subjects need to be added to the acl for each realm in our example:

The permissions given for each realm need to be 'Access Realm'. As well as this, each realm must have a valid entry for the user@host that corresponds to the user that will create the cluster using the Enterprise Manager. The permissions for this user must be sufficient in order to create the cluster object. Temporarily it is often better to provide the *@* default subject 'Full' privileges to facilitate setting up a realm and clusters.

If you select the 'Clusters' node under the 'Universal Messaging Enterprise' node, you will be shown a pop up menu with a number of options. One of the options is to create a cluster. The image below shows this menu option as described.

When you select the 'Create Cluster' menu option, you are presented with the cluster dialog. The cluster dialog allows you to select which of the realms that the Enterprise Manager is connected to will become members of the cluster. One of the selected realms will become the master during the cluster creation. The master realm will controls synchronizing the state between the other realms and acts as the authoritative source for this information.

The cluster dialog contains a text box for you to input the name of the cluster. Below the name, are the details of the cluster members. The available realms are shown on the left hand side of the dialog. The right hand side shows those realms that are members. When you double-click on a realm name, or click on a realm name and click on the 'Add' button, the realm will be added to the Cluster Members list. You can remove any realm from either the Cluster Members list by either double clicking on the realm from the list or by selecting the realm name, and clicking on the 'Remove' Button.

When you have finished selecting your cluster members, clicking on the 'OK' button in the Cluster dialog will create the cluster. A new cluster node will appear under the 'Clusters' node and the realms that have been selected as members will be rendered beneath the cluster.

When a cluster has been created, you can monitor its state by selecting the cluster node. The 'Cluster Summary' tab will show the state of all cluster members, and which realm is current cluster master. The image below shows the state of a cluster when it has been created and all realms within the cluster are fully online.

Creating cluster channels (see Cluster Channel Administration) and cluster queues (see Cluster Queue Administration) is not permitted if any of the cluster realms are offline.