Dockerfile best practice

[leshikus]

Hey @alexbaden

Igor has sent me a link to the https://github.com/intel-ai/hdk/blob/main/docker/Dockerfile#L3

IMO The docker best practice is to use apt-get update each time you call apt-get install in a separate RUN, this is because /var may not be properly updated if the docker is reconstructed from cached layers.

FROM ubuntu:20.04

ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get clean

# Tools
RUN apt install -y ca-certificates

Here is a small example which does not work because it does not have the index files. If the index is obsolete, the problem will happen if the package version is updated.