[DRAFT][Dockerfile] Minimize the number of image layers

[yelghali]

Docker images work in the following way – each RUN, COPY, FROM Dockerfile instructions add a new layer & each layer adds to the build execution time & increases the storage requirements of the image.

minimizing the number of layers can significantly reduce image size and container build time.

bad example:
FROM ubuntu:latest
ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update -y
RUN apt-get upgrade -y
RUN apt-get install vim -y
RUN apt-get install net-tools -y
RUN apt-get install dnsutils -y
COPY . .

good example:
FROM ubuntu:latest
ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update -y && apt-get upgrade -y && apt-get install --no-install-recommends vim net-tools dnsutils -y

To help you make your container smallers and more optimized, you can use tools like: https://github.com/slimtoolkit/slim