- [Instructor] A huge portion of this course,
and an important part of
the Docker Certified Associate exam blueprint,
is image creation and management.
So let's start off by answering a basic question.
What exactly is a Docker image?
Well, according to the Docker documentation,
an image is an executable package that includes
everything needed to run an application,
including the code, a runtime, libraries,
environmental variables and configuration files.
And the documentation goes on to state that
a container is a runtime instance of an image.
I'll put it into fewer words.
Essentially an image is a container that's not yet running.
So if you were to download a container,
you don't actually download the container,
you download the image and then you run the container.
Let's examine what a Docker image is,
in a little bit more visual way.
If we start off with your computer,
and on your computer you have installed Docker.
Inside Docker you have images.
These images are the stopped containers.
You've downloaded these images most likely
from the Docker registry out on the internet.
Or perhaps from a private registry at your company.
These images are read only.
Meaning you can't change these images.
You can build new images, based on those images.
But you don't run those images,
and you don't change or modify those images.
When you instantiate an image, or run an image,
that becomes a container.
So a container is essentially a running image.
In this course we'll be focusing in on images.
We'll talk about how you can tag images,
or label images, run images, build images,
using Docker files, push images up to registries,
and pull images down from registries.
So that's what a Docker image is.
Now Docker images are made of layers.
Let's talk about that.