Events are key to fast data delivery
To deliver data fast, using a method that's cheap and easy to scale, application developers put data into event messages whenever something noteworthy occurs in their applications. The event messages are saved to storage. Applications, such as microservices, can then read event messages in real-time, apply rules (business processes) to the events, to produce aggregated data. This data is fast to access because it's already aggregated and is typically stored in memory. Scaling out is as easy as installing copies of the microservices on additional servers.
Event messages store data about what happened.
Rules and Aggregates
Rules process data in event messages to produce aggregated data.
Snapshots help aggregates load into memory faster.
Sequence numbers can tell us when data is ready for reading.