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Docker Terms Review
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.. contents:: Table of Contents

You've seen how to use a docker image directly using ``docker run``
and using a ``docker-compose.yml`` file. Both methods do the same thing,
which is to create a container from a Docker image. Now, let's take a
look at how to build a Docker image.

Let's review some Docker terms before we continue. These terms are from
|dotnet doc's terminology| page. See additional terms and examples on page
|A Practical Introduction to Docker Container Terminology| provided by Redhat.

Image
    *A package with all the dependencies and information needed to
    create a container.*

    A container represents a runtime for a single application,
    process, or service. It consists of the contents of a Docker image,
    a runtime environment, and a standard set of instructions. When scaling
    a service, you create multiple instances of a container from the same
    image. Or, a batch job can create multiple containers from the same
    image, passing different parameters to each instance.

Container
    *A read-only instance of a Docker image.*

    A container represents the execution of a single application, process,
    or service. It consists of the contents of a Docker image,
    an execution environment, and a standard set of instructions.
    When scaling a service, you create multiple instances of a container
    from the same image.

Volumes
    *A writable filesystem that the container can use.*

    Images are read-only but most programs need to write to the filesystem.
    Volumes add a writable layer on top of the container image so that
    programs can access a writable filesystem.

Dockerfile
   *A text file that contains instructions for how to build a Docker image.*

Build
    *The action of building a container image using the information
    in a Dockerfile.*

Tag
    *A mark or label that you can apply to images for identification*.

Repository (repo)
    *A catalogued or indexed collection of Docker images.*

Registry
    *A service that provides access to repositories.*

    The default registry for most public images is |Docker Hub|
    (owned by Docker as an organization).

Docker Hub
    A public registry of images.

    ``docker run``, ``docker-composer``, and ``Dockerfile`` use images
    from |Docker Hub|. For example, ``docker run`` downloads ``nextcloud``
    from Docker Hub before it creates the container using this command:
    ``docker run -d -p 80:80 nextcloud``.

Multi-arch image
    *An image designed for multi-architecture systems*.

Compose
    *A command-line tool and YAML file format with metadata for
    defining and running multi-container applications*.

.. |A Practical Introduction to Docker Container Terminology| raw:: html

   <a href="https://developers.redhat.com/blog/2016/01/13/a-practical-introduction-to-docker-container-terminology/" target="_blank">A Practical Introduction to Docker Container Terminology</a>

.. |dotnet doc's terminology| raw:: html

   <a href="https://github.com/dotnet/docs/blob/master/docs/standard/containerized-lifecycle-architecture/docker-terminology.md" target="_blank">dotnet doc's terminology</a>

.. |Docker Hub| raw:: html

   <a href="https://hub.docker.com/" target="_blank">Docker Hub</a>