Images

What's in an Image (And what isn't)

• App binaries and dependencies

• Metadata about the image data and how to run the image

• Official definition:

  • "An Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime"

• Not a complete OS. No kernel, kernel modules (e.g. drivers)

• Small as one file (your app binary) like a golang static binary

• Big as a Ubuntu distro with apt, and Apache, PHP, and more installed

Layers

• Images are made up of file system changes and metadata

• Each layer is uniquely identified and only stored once on a host

  • This saves storage space on host and transfer time on push/pull

• A container is just a single read/write layer on top of image

Union Filesystem

• Based on layers of changes

Official Repositories

They live at the "root namespace" of the registry so they don't need account name in front of repo name

• When uploading to DockerHub you need to be first logged in. You can do that with:

docker login            # logs you in to DockerHub
docker logout           # always logout on shared machines or servers

External

• Official Docker Image Specification

• List of Official Docker Images

• Images and Containers From Docker Docs