To answer your last question; let’s say I have some shared state that multiple micro-services rely on and all need to fetch that state synchronously. My example is that you’re a loans company and almost everything is driven from the loan book. Reporting services need to know the active loan counts this month, invoicing services need to fetch the loan book to generate transaction lines, borrower services need to know whether the current user has any active loans.

The standard wheel-and-spokes model would probably have a loan book service where all others call into it via HTTP requests, but you’ll have to build a query language on top of that REST API, or share DB access I suppose.

Or in this model you would stream the loan book updates through Kafka and every consumer that needs a copy of the loan book can keep their own, query it against their own chosen materialised store in its native query language (some might just append to Mongo, or kSQL, some might always use event sourcing per-request). “select * from loans where user.id = current_user” becomes possible here rather than stitching the HTTP responses.

Now I’m not saying one is right or wrong outright as you’re only trading a more native query interface with data consistency concerns, but this for me still feels like a valid architectural pattern and one I’d consider.