SQL Server Integration Services (SSIS) - Event Handlers
Like any other event driven programming language, SSIS package and its components also generate events in their execution life-cycle. You can extend package functionality by writting event handlers for these events and can make package management easier during runtime.
I have written an article covering all aspects of SSIS Event Handler functionality, starting with what Event Handler is, examples of some events, it usage scenarios, its configuration and finally best practices to follow while using this feature.
Refer this link for more details.