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CHAPTER 1 | Introduction to Containers and Docker
2.
To issue a set of letters, you pick the sheets with the paragraphs you need, then you stack and
align them so they look and read fine.
3.
Finally, you place the set in the photocopier and press start to produce as
many letters as
required.
So, simplifying, that’s the core idea of Docker.
In Docker, each layer is the resulting set of changes that happen to the filesystem after executing a
command, such as, installing a program.
So, when you “look” at the filesystem after
the layer has been copied, you see all
the files, included in
the layer when the program was installed.
You can think of an
image as an auxiliary read-
only hard disk ready to be installed in a “computer”
where the operating system is already installed.
Si
milarly, you can think of a container as the “computer” with the image hard disk installed. The
container, just like a computer, can be powered on or off.
Docker terminology
This section lists terms and definitions you should be familiar with before getting deeper into Docker.
For further definitions, see the extensive
glossary
provided by Docker.
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