Contain Yourself: Basic Docker Terminology

If you've heard different key terms for Docker's building blocks but don't fully grasp what they mean, we've prepared this list to help act as a reference and keep a mental image of what's going on.

To start, Docker borrows concepts from the shipping container industry, and knowing this helps to remember how the components fit together.

Image:

Docker images are the basis of containers. An Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. An image typically contains a union of layered filesystems stacked on top of each other. An image does not have state and it never changes.

Shipping Container Analogy:

Think of an image as a blueprint, or a manifest which might list what goes in to a container, and how it's contents are organized.

Containers

A container is a runtime instance of a docker image.

A Docker container consists of:

  • A Docker image
  • An execution environment
  • A standard set of instructions

Shipping Container Analogy:

The concept is borrowed from Shipping Containers, which define a standard to ship goods globally. Docker defines a standard to ship software.

There are many docker terms and concepts and we might expand this list as we go.

For an exhaustive list of definitions, see Docker's full glossary:

https://docs.docker.com/glossary/