An image is
a lightweight, stand-alone, executable package that includes everything needed
to run a piece of software, including the code, a runtime, libraries,
environment variables, and config files.
A container is
a runtime instance of an image—what the image becomes in memory when
actually executed. It runs completely isolated from the host environment by
default, only accessing host files and ports if configured to do so.
Containers
run apps natively on the host machine’s kernel.
Docker daemon - The background service running on the host that manages
building, running and distributing Docker containers.
Docker client - The command line tool that allows the user to interact
with the Docker daemon.
Docker Store - A registry of Docker images, where you
can find trusted and enterprise ready containers, plugins, and Docker editions.
You'll be using this later in this tutorial.
An important distinction with regard to images is between base
images and child images.
·
Base images are images that
have no parent images, usually images with an OS like ubuntu, alpine or debian.
·
Child images are images that
build on base images and add additional functionality.
Another key concept is the idea of official images and user
images. (Both of which can be base images or child images.)
·
Official images are Docker
sanctioned images. Docker, Inc. sponsors a dedicated team that is responsible
for reviewing and publishing all Official Repositories content. This team works
in collaboration with upstream software maintainers, security experts, and the
broader Docker community. These are not prefixed by an organization or user
name. In the list of images above, the python, node, alpine and nginx images are official (base)
images. To find out more about them, check out the Official Images Documentation.
·
User images are images created
and shared by users like you. They build on base images and add additional
functionality. Typically these are formatted as user/image-name. The user value in the image name is
your Docker Store user or organization name.
A
registry is a collection of repositories, and a repository is a collection of
images
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