Operating a product built on somebody else's model.
Notes on the specific discipline of running a product whose core capability belongs to another company: what to log, what to publish, and how to tell your users about a change you did not make and were not warned about.
It is a small field and almost nothing is written about it, largely because the people doing it are busy.
When the interesting failures happen inside somebody else's service, your logs are the only evidence you will ever get. Most teams find this out late.