Docker Inc., the company behind popular container engine, aims to move code for building images out of server. The component is named builder currently and is available at URL /build in daemon’s API. It is the most common and official method of building images.

Upstream already managed to implement all low-level API calls which were needed to create an image (these were used internally by build API call). These functions are:

• create and start container
• commit container – transform a container to an image (this call is able to change metadata also)
• copy files or folders inside a container
• tag an image

Builds in current state suffer from multiple issues which docker is not planning to address any time soon: having secrets during build time which won’t leak to final image, controlling number of layers in final image, precisely specifying metadata of a final image and more.

Target of this thesis is to research and implement a solution, which uses engine API endpoints mentioned above (/commit, /containers/(id or name)/archive, /containers/(id or name)/exec). The tool should be able to:

• Build an image from provided dockerfile.
• Mount a directory inside container during build with arbitrary data (e.g. private ssh keys) which won't be present in final image.
• Precisely control layering of the final image.
• Enable to add arbitrary metadata to the image
• The tool should be written in Python programming language and should support both version 2 and version 3.