It is expected that business solutions, whether designed in accordance with the Service Oriented Architecture principles, or designed following any of the other accepted architectural principles, are robust, reliable and available. Robustness, reliability and availability, in this context, means not just that solutions are free of design and implementation defects but are also architected and deployed in such a way that business users can access them when needed, in spite of any failures that may occur.
In an ideal world all applications will always be available for use. In the real world this may not be possible, or may not be possible at a reasonable cost.
The document referenced below discusses resilience options available to the designers of GlassFish ESB solutions and considerations that need to be entered into when designing GlassFish ESB solutions for resilience and high availability.
The document, GlassFishESB_Solution_Resillience_Options_v0.5.pdf, is available at http://blogs.czapski.id.au/wp-content/uploads/2010/03/GlassFishESB_Solution_Resillience_Options_v0.5.pdf