Delete the apt-get lists after installing something DOK-DL3009

[philipjonsen]

DESCRIPTION
Cleaning up the apt cache and removing /var/lib/apt/lists helps keep the image size down. Since the RUN statement starts with apt-get update, the package cache will always be refreshed prior to apt-get install. You can read more about it here: https://docs.docker.com/develop/develop-images/dockerfile_best-practices/

Note: Clean up must be performed in the same RUN step, otherwise it will not affect image size.

Problematic code:

RUN apt-get update && apt-get install -y python

Correct code:

RUN apt-get update && apt-get install -y python
&& apt-get clean
&& rm -rf /var/lib/apt/lists/*