About Exception Events
An exception event occurs when a service throws an exception (including when a flow service “exits on failure”). You can use exception events to invoke some prescribed action, such as notifying an administrator, when a particular service fails.
Note:
Keep in mind that event handlers are processed independently of the services that invoke them. Event handlers are not designed to replace the error handling and/or error recovery procedures that you would normally include in your service.
If a nested service throws an exception, an exception event is generated by each service in the call stack. For example, if service A1 calls service B1, and B1 throws an exception, both B1 and A1 generate exception events (in that order).