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


  • 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


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