Google_app_engine_flexible_app and app.yaml


I’m very new to GCP but have worked a lot of terraform AWS.

I’ve deployed an app engine app with gcloud and an app.yaml. I assumed there was a way to feed that to terraform but seems as though there is not. However, one can build up a resource with the parameters within app.yaml (eg: beta settings, resources, service)

Why, then, does the apply complain when there is no app.yaml - given that these params are passed to terraform already? Why are we passing them to tf, I guess, if app engine needs the yaml?