Eventual Consistency

Eventual consistency is constant in distributed applications and especially in event-driven applications. It is a trade-off made for the performance and resiliency gains when choosing to architect a system with asynchronous communication patterns. Here’s a quick definition of what eventual consistency is:

Note: An eventually consistent system that has stopped receiving modifications to an item will eventually return the same last update across the system.

There is a good chance that if we are working with microservices and using synchronous communication patterns, we are at least aware of and somewhat comfortable with eventual consistency. If we are working with a monolith—even a modular monolith such as our little application—we might not be aware of or comfortable with it.