WS-Notification and end-to-end reliability
Reliable notification refers to the reliable transmission of messages to and from the IBM WS-Notification implementation. You enable this reliability to mitigate the problems inherent in network transmission protocols such as HTTP.
Figure 1. How a notification message is passed reliably
A notification message is passed from a producer application across the Internet to a WS-Notification service point, by using SOAP over HTTP. The WS-Notification service point publishes the message to a topic configured on the underlying service integration bus, which is associated with one or more application servers. The bus routes the message (potentially across a LAN, WAN or Internet) to any WS-Notification service points at which there are subscriptions made on behalf of external WS-Notification consumers. The receiving WS-Notification service points pass the message across the Internet to WS-Notification consumer applications, again by using SOAP over HTTP. Reliability is provided for the WS-Notification web service interactions by WS-ReliableMessaging, and when the message is passing through the service integration bus, reliability is provided by the bus itself.
When the message is being processed by a WS-Notification service point, control is briefly passed to the application server. There is a very brief vulnerability when this occurs, and if there is a major system failure at the precise moment that the message is being processed by the WS-Notification service point, it is possible for a message to be lost or duplicated.
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