My problem is that I want to create `dev`, `stage`, `prod` environments by using different GCP projects. 

Basically they are running the same code, just running them in different isolated environments. 

I'm using `gcloud app deploy` in command line to deploy app right now.

How can I efficiently deploy an app to different project?  

Do I have to do `gcloud init` to change my configuration of default project every time?  

There must be some better practices. 

Or, is there a better way for me to set up `dev`... environments in the context of app engine?

Thanks.