Php – How to connect to Cloud SQL MySQL database from App Engine

I believe there is no actual need for you to be touching Nginx. The link you are basing yourself on has to do with the HTTP Load Balancer, not with App Engine Flexible.

An example of working Django application on App Engine flexible may be found here.

Perhaps this is useful for someone else who encounters this. It is certainly advisable to use @George's answer for normal operation, but in a pinch you can shell into run a python command from App Engine. I recently had to for debugging purposes. I used the SSH access in App Engine -> Instances in the GCP Control Panel. In my case I was using the flex environment which runs docker inside an VM instance so there are a few steps.

1. Go to GCP -> Engine -> Instances and SSH into an instance.
2. Once an SSH session is running make sure your containers are running: docker ps. In my case my Django app was running in a container called gaeapp.
3. Docker exec into the container: docker exec -it gaeapp /bin/bash
4. If that command works you are now in a running container for your app. Run your command. For example: python manage.py help

NOTE: These environments should be considered ephemeral and you should not make this part of any consistent workflow. When an App Engine instance is changed from debug mode back to normal operation it is very likely it will be destroyed and a new instance will replace it. This means any files generated will be lost. It also means any files generated will only exist on one of potentially many VM instances.