As an ESB based SOA is implemented within a large organisation, it is inevitable that multiple (logical and physical) Enterprise Service Buses will be deployed. It is important to consider how these ESB's will actually be managed.
The mere existence of multiple ESB's introduce a variety of challenges related to architecture, configuration and monitoring. To complicate matters, the issue of ESB platform must be considered. What is the likelihood of all of the ESB's in a large organisation being implemented using a single product? The reality is that for a variety of reasons, multiple products are likely to be deployed. When developing an SOA strategy, it is wise to assume that there will be multiple ESB products deployed
The diagram shows a number of services and clients associated with 4 ESB's. The primary architectural question can be illustrated by considering how messages might be routed between a requester on ESB 2 and a service on ESB 3. The logical choices are: