The lifespan of events: why evolution matters
Event-sourced systems, being an append-only model, are subject to versioning issues, and you must handle them effectively to ensure the system’s long-term viability. Events, once written to the event store, are immutable and represent a historical record of what has occurred in the system. This immutability is a core strength of event sourcing, providing a complete audit trail and the ability to reconstruct the state from past events. However, the immutability of events also introduces challenges when the structure or meaning of events needs to evolve, as older events must coexist with newer ones in the same system. Since aggregates rely on replaying historical events to reconstruct the state, they must remain compatible with all previous event versions.
In traditional systems, managing changes to a database schema is often straightforward. You apply a schema update script, and as long as you add columns or make non-breaking...
