I start at the controller and read outward, but what taught me the service was the jobs. Controllers told me what the API allows, the workers told me what the thing does when nobody is watching: retries, partial writes, the states nobody modelled. So now I read the controller for the shape and then follow one request all the way through a queue to the table.

My first pass on a service like this is usually wrong in the same way, I mistake the entry point for the design.