The members of a service integration bus are application servers. Bus members that are application servers contain messaging engines, which are the application server components that provide asynchronous messaging services.
To use a service integration bus, you must add at least one member that is an application server.
Adding a bus member automatically creates a messaging engine for that bus member. Each messaging engine has its own data store, used for example to store persistent messages and maintain durable subscriptions. By default a messaging engine associated with a server is configured with an in-process, Cloudscape-based data store. In other cases, you are asked to provide the Java™ Naming and Directory Interface (JNDI) name of a Java Database Connectivity (JDBC) data source for use by the messaging engine.
When the bus member is an application server, it can have only one messaging engine.
To host queue-type destinations, the messaging engine can hold messages until consuming applications are ready to receive them. Each messaging engine also has a data store where it can hold messages so that if the messaging engine fails, messages are not lost.
When you define a queue-type destination, you assign it to a bus member. When that bus member is an application server, the messaging engine in that bus member holds the messages.
A WebSphere® Application Server application does not have to be running on a service integration bus member to use its messaging services. If necessary, WebSphere Application Server automatically provides a connection to a suitable bus member.
If required, you can remove members from a bus. However, this action deletes any messaging engines that are associated with a bus member, including knowledge of any messages held by the data store for those messaging engines. Therefore, you must plan this action carefully.
When a bus member is deleted, the data source associated with this bus member is not automatically deleted, because users often associate their own data source with a bus member. This also applies to bus members created using the default data source: the data source is not automatically deleted and you must remove it manually.
If you do not delete the data source manually and another messaging bus member is created, the messaging engine will fail to start.
Server clusters can be used as bus members only in WebSphere Application Server environments that support server clusters.