On the standard env, we can set up "threadsafe: yes" in app.yaml to enable multiple threading for flask framework in python. Because Google will do anything for us.
For flexible env, we need to setup gunicorn to enable async-worker to make an application can process more than one request at one time.
But I wonder why the parameter "threadsafe: yes" does not work on flexible env and Google does not give us any error msgs when deploying the app engine.
app.yaml
runtime: python
env: flex
api_version: 1
threadsafe: yes --> Is this working ?
service: myapp
entrypoint: gunicorn -b :$PORT main:app