the image is not there, the daemon asks the registry for
the image file and then stores it locally.
The registry is a place to store container images; it is also
known as the repository for the container infrastructure.
You can pull images from a registry to run or push new
images you create yourself to the registry for storage.
Then other hosts in your container environment can
make use of your new container image. A registry can be
private, for the sole use of a single organization, or
public, as in the case of Docker Hub.
USING DOCKER
The best way to get familiar with Docker is to use it.
Download the appropriate version of Docker for your
computer and launch its containers. It is available for
both macOS, Windows, and Linux allowing you to install
the Docker engine and command-line tools directly on
your local machine.
Note
As of version 1.13, Docker has changed the command
line to include a more logical grouping for people just
getting started. If you are familiar with the old-style
command line, fear not, those commands still work.
The additions of the management command syntax
just add a hierarchy that will differentiate what you are
working on instead of everything being lumped
together. This book uses the new Docker command
structure. If you were to get a question on the exam
that uses the old command line, you could simply omit
the first command after docker. For example, the
command docker container ps would be shortened
to docker ps.