A container only knows about what's going on inside it though. If you want to hook those resources up with peers in a decoupled way, that requires an abstractio

A container only knows about what's going on inside it though. If you want to hook those resources up with peers in a decoupled way, that requires an abstraction on top, preferably declarative, or else you faced with a substantial amount of manual (and thus costly and error-prone) management. We could argue the merits of yaml and I'll happily concede it's not ideal, but the complexity isn't going away and the tools to manage it are pretty standard.