You are right. Either you are using docker very wrong, or docker is not meant for this use case.

You say “getting ubuntu server to fetch it’s updated behind proxy”. You shouldn’t be updating Ubuntu from inside of docker. Instead, the system should be somewhat immutable. You should configure the version you want to use as part of the Docker file.

Same with python and keys. You likely want to install python dependencies in the Dockerfile, so that you can install them once and it becomes bundled into the container image. Then you don’t need to use pip behind the proxy.

This mindset is carried “techno-wizard”