It is better to run components in separate containers instead of one container that runs everything together. You'll likely have a single proxy but multiple copies of application. Also, you don't need to deal with getting Envoy and Python application built together, or even care about how the Envoy image is built since you can use the provided one.
If I wanted to run a Python app, which serves gRPC, what would be the easiest path?
I currently use nghttp2 for gRPC proxy/routing