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Learning Docker: Getting the Names Right

  |  May 21, 2014

I started reading about Docker last October and introduced it to our local Ruby meetup a month later. I’ve put it aside and picked it up again after the release candidate was announced.

One of the things I’ve struggled with learning this tool is not having a good mental model of the terms used in the documentation.


An image is your application code, including anything that it needs in order to run. This serves as a template for containers.

A container is an instance of an image. You can start, stop, and inspect a container.

Images can be shared to an index. You can pull images from a public or a private index.

To check which containers are running in your docker machine, run this command:

docker ps
In order to run a container, you will need an image. The Docker Index hosts these commonly used images (e.g. ubuntu):
docker pull ubuntu
An image consists of a series of changes made to a filesystem, called layers. Docker downloads these layers if they are not already present in your docker machine.

Recommended Reading

Understanding Docker