An event is both a fact and a notification, something that already happened in the real world.

  • No expectation on any future action

  • Includes information about a status change that just happened

  • Travels in one direction and it never expects a response (fire and forget)

  • Very useful when...

    • Loose coupling is important

    • When the same piece of information is used by several services

    • When data needs to be replicated across application

A message in general is any interaction between an emitter and a receiver to exchange information. This implies that any event can be considered a messages but not the other way around.

There are several ways to use events in a EDA:

  • Events as notifications

  • Events to replicate data

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