How to deploy a Docker image to make changes in the local environment?

Question

EDIT +2=Just fyi, i am a root user which means i do not have type out superuser do (sudo) every time i do a authorized only cmd.

Alright so after about 24 hours of researching Docker i am a little upset if i got my facts straight.

As a quick recap, docker serves as a way to write code or configuration file changes for a specific web service, run environment, virtual machines, all from the cozy confines of a linux terminal/text file. This is beyond a doubt an amazing feature: to have code or builds you made on one computer work on an unlimited number of other machines is truly a breakthrough. While i am annoyed that the terminology is wrong with respect to whats containers and what are images (images are save points of layers of code that are made from dockers servers or can be created from containers which require a base image to go off of. Dockerfiles serve as a way to automate the build process of making images by running all the desired layers and roll them into one image so it can be accessed easily.).

See the catch is with docker is that "sure it can be deployed on a variety of different operating systems and use their respective commands". But those commands do not really come to pass on say something like the local environment though. While running some tests on a dockerbuild working with centos, the basic command structure goes

FROM centos
RUN yum search epel
RUN yum install -y epel-release.noarch
RUN echo epel installed!

So this works within the docker build and says it succesfully installs it. The same can be said with ubuntu by running an apt-cache instead of yum. But going back to the centos VM, it DOES NOT state that epel has been installed because when attempting to run the command of

yum remove epel-release.noarch

it says "no packages were to be removed yet there is a package named ...". So then, if docker is able to be multi-platform why can it not actually create those changes on the local platform/image we are targeting? The docker builds run a simulation of what is going to happen on that particular environment but i can not seem to make it come to pass. This just defeats one of my intended purposes of the docker if it can not change anything local to the system one is using, unless i am missing something.

Please let me know if anyone has a solution to this dilemma.

EDIT +1=Ok so i figured out yesterday what i was trying to do was to view and modify the container which can be done by doing either docker logs containerID or docker run -t -i img /bin/sh which would put me into an interactive shell to make container changes there. Still, i want to know if theres a way to make docker comunicate to the local environment from within a container.

Answer 1

So, I think you may have largely missed the point behind Docker, which is the management of containers that are intentionally isolated from your local environment. The idea is that you create containerized applications that can be run on any Docker host without needing to worry about the particular OS installed or configuration of the host machine.

That said, there are a variety of ways to break this isolation if that's really what you want to do.

You can start a container with --net=host (and probably --privileged) if you want to be able to modify the host network configuration (including interface addresses, routing tables, iptables rules, etc).

You can parts of (or all of) the host filesystem as volumes inside the container using the -v command line option. For example, docker run -v /:/host ... would expose the root of your host filesystem as /host inside the container.

Normally, Docker containers have their own PID namespace, which means that processes on the host are not visible inside the container. You can run a container in the host PID namespace by using --pid=host.

You can combine these various options to provide as much or as little access to the host as you need to accomplish your particular task.

If all you're trying to do is install packages on the host, a container is probably the wrong tool for the job.