Is there already a project out there that does docker-based continuous integration?
* With docker build you can automate the building of a docker container from source. Simply add a Dockerfile to your source to specify exactly how to assemble it, step by step. This can be done with the high-level build or configuration tool of your choice.
* With docker history you can point to any docker container and get a full record of exactly how it was built.
* We are adding image signature to allow verification of the origin of any particular container image.
If I understand correctly, this is only up to the base image. All the docker docs talk about basing images from well known images from the index. I'd very much like to know how "ubuntu" is prepared for example.
The source, in turn, can either 1) specify a base image to start from (keeping in mind the base image can recursively be itself built from source), or 2) start from scratch and contain all the starting bits.
Of course there is always a "turtle at the bottom". That problem exists regardless of Docker - for example when you download binary packages from an apt mirror, that package has been built from source - but on which build environment exactly, with which build dependencies etc? Docker simply makes this question more explicit by forcing you to ask that question every step of the way - what is the base? - instead of sweeping it under the rug, which we do every day when we install binary packages.
What we're doing for the docker standard library is exposing exactly what the turtles at the bottom are: https://github.com/dotcloud/stackbrew/tree/master/library