Yep, this has been my experience as well. When micro services work well they have a simple and well-defined API that is easy to keep backwards compatible as it

Yep, this has been my experience as well. When micro services work well they have a simple and well-defined API that is easy to keep backwards compatible as it evolves, and it tends to be something that evolves quite slowly compared to the primary application codebase. For the posters who said "like a library," yeah that's exactly the idea, but consider if you have an operation that can be done by a library but that has very different scaling characteristics compared to the rest of your system. Eg. you have one highly compute intensive operation while the rest of your system is IO bound. If you can split these apart it's easier to deal with scaling.