In this architecture, events are a persistence strategy. Once created, they are saved forever, so if they get dropped, it calls for an investigation and a resto

In this architecture, events are a persistence strategy. Once created, they are saved forever, so if they get dropped, it calls for an investigation and a restore from backup. Having worked with such a system before, the real pain is that any data exposed by one microservice to another becomes an API, and it is very hard to design events that are both a good public API and a private data persistence system. Immutability means consumers of your API will need to understand, and deal with, obscure concepts and business rules from five years ago, because those events are still around. One of the major points of an API is to hide private complexity behind a public abstraction that you can design and update as needed.