A service integration bus that consists of multiple servers provides advantages of scalability, the ability to handle more client connections and greater message throughput. You can also deploy SCA modules to different servers; for example, to provide different resources and qualities of service, or to provide some separation for different departments within organizations, or perhaps to separate test and production facilities.
You can configure a service integration buses to have multiple server bus members, each of which runs one messaging engine.
To create more than one server in your bus environment, you need to have a managed node in a deployment manager cell. When you create a new ESB server, you can choose to add it to an SCA.SYSTEM bus and condition it for SCA use.
All of the messaging engines in the SCA.SYSTEM bus are implicitly connected, and requests can be processed by any messaging engine in the bus. Knowledge of the resources assigned to each messaging engine in a bus is shared between all the messaging engines in the bus.
There is no requirement for all the messaging engines in the bus to be running at the same time; if one of the messaging engines is stopped, the rest of the messaging engines continue to operate. However resources owned by a messaging engine, specifically queue points for SCA modules assigned to that messaging engine, are unavailable if the engine is stopped. Also, a messaging engine can only run in the server it was created for. The server is therefore a single point of failure; if the server cannot run, the messaging engine is unavailable. By configuring a server cluster as a bus member, a messaging engine has the ability to run in one server in the cluster, and if that server fails, the messaging engine can run in an alternative server within the cluster.