title: Docker image format
body: <p>I would like to build a Docker image without docker itself. I have looked at [Packer](<a href="http://www.packer.io/docs/builders/docker.html" rel="nofollow noreferrer">http://www.packer.io/docs/builders/docker.html</a>, but it requires that Docker be installed on the builder host.</p>
  <p>I have looked at the <a href="https://docs.docker.com/reference/api/registry_api/#image" rel="nofollow noreferrer">Docker Registry API documentation</a> but this information doesn't appear to be there.</p>
  <p>I guess that the image is simply a tarball, but I would like to see a complete specification of the format, i.e. what exact format is required and whether there are any metadata files required. I could attempt downloading an image from the registry and look what's inside, but there is no information on how to fetch the image itself.</p>
  <p>The idea of my project is to implement a script that creates an image from artifacts I have compiled, and uploads it to the registry. I would like to use OpenEmbedded for this purpose, essentially this would be an extension to Bitbake.</p>