I understand the basic architecture (or so I think) and its again the question of what happens when you have lots of complex entities with complex workflow/sign

I understand the basic architecture (or so I think) and its again the question of what happens when you have lots of complex entities with complex workflow/significance. For example in banking the transactions is one core thing while the rest of customer information is not so much, same goes for a the shipping example (or at least it looks that way from the outside). In a health scenario on the other hand I can see most information being required being the type that require an ES model. What I gather from Kafka style architecture is the storing/persistent works through the abstraction the processing itself you have to do separately for each type of entity and if you have many of them and your query requirement are complex not sure how to abstract that. I might be missing something. Again the idea of caching, lazy updating, horizontal scaling those resonates with me but I don't see how to write good abstractions that allows to apply that. For most complex entities it seems I have to do this case by case basis and I can't figure out ways to contain/manage that complexity. And while ES adds for write scalability transactional integrity seems to become much more a complicated questions and hard to abstract about, doesn't it?