Hi @j_buddy13, welcome to the Streamlit community!
From my reading of the comparison between the two GCP environments 2, it looks like the flexible environment is needed because Streamlit uses websockets.



 j_buddy13:


Why is a container necessary?



I’m not sure a container is actually required, but that it gives you more flexibility. It seems like only Python 3.6 is available in the flexible environment and so if that’s okay with you, you might be able to get away without using Docker.



 j_buddy13:


Is there an official Streamlit tutorial for launching the “hello world” streamlit app on App Engine?



There isn’t. We’ve put together the Streamlit Deployment Wiki 23 to try and surface the best examples from the community. But with the number of different services where you could deploy a Streamlit app, it would be difficult for us as a company with the current level of staffing to provide detailed instructions for every environment.
Best,
Randy