The business logic simply outputs state changes that other systems subscribe to. If the subscribing system misses the update our reliable message delivery will ensure the message gets to the subscribing system and processed. Our system guarantees message processing and not just delivery.

Queries against the business domain model are just input events. The business logic will serialise the requested part of the model and publish it out. This type of query can easily be handled by any number of replica nodes.

All messages in the system carry a sequence number so duplicate messages can be detected and ignored.