This configuration consists of a single messaging engine, running in a cluster, which can fail over to one or more alternative servers.
You can achieve this configuration by adding a cluster to the service integration bus. This procedure creates a single messaging engine for the cluster. The messaging engine uses the default SIBus core group policy with default properties, such that the messaging engine can fail over to any server in the cluster. You can optionally create a new core group policy for the new messaging engine and give the messaging engine a preference for one or more servers, by adding preferred servers to the policy. You can further alter the policy to control the availability characteristics of the messaging engine, as described in Configuring a policy for messaging engines. It is not advisable to change the default SIBus core group policy.
There is no workload sharing in this configuration, because there is only one messaging engine to handle the traffic through the destination.
The following diagram shows a highly available messaging engine configuration in which a single messaging engine, ME, with data store DS, runs in a cluster of three servers. When Server-1 fails, the messaging engine fails over and continues to run on Server-2.
Each server in the cluster contains the definition of the messaging engine, and creates an instance of the messaging engine so that the instance is ready to be activated if another server fails.
The data store for the messaging engine must be accessible by all the servers in the cluster. How to do this depends on the data store topology that you use. If you use a networked database server, ensure that it is accessible from all servers in the cluster that might run the messaging engine. Alternatively, you could use an external high availability framework to manage the database using a shared disk.
You can specify one or more preferred servers for the messaging engine, as mentioned earlier. Whenever a preferred server is available, the HAManager will run the messaging engine in it. When no preferred server is available, the messaging engine will run in an alternative server. When a preferred server once again becomes available, the HAManager will move the messaging engine back to it if, and only if, the Fail back option is set on the policy.