> Docker includes git-like capabilities for tracking successive versions of a container, inspecting the diff between versions, committing new versions, rolling back etc. The history also includes how a container was assembled and by whom, so you get full traceability from the production server all the way back to the upstream developer. Docker also implements incremental uploads and downloads, similar to git pull, so new versions of a container can be transferred by only sending diffs.
I get it now. They support features which are comparable to features found in Git. Similar to how Apt and RPM are just like Git, because they also have the same features.
What I don't see is specifically git-like functionality, which would be incredibly useful for anyone who packages deployments of OSes, applications, configs, etc. For example, with Git you have a workspace that allows you to work with a tree of files, make changes, make specific commit logs for specific changes, merge, compare, search, etc. From what I see of docker, it's all just "how do I move my already-built containers around" functionality, and of course a shell-script (or specfile, or debian rules file) replacement called a Dockerfile.
There are lots of deployment solutions out there. What there isn't is a handy way to manage and track the assembling and customization of your various things-to-be-deployed, independent of the platform. A deployment tool that did that would become very popular.
Have you actually tried Docker? It does exactly what you describe.
Docker containers are versioned similarly to git repositories. You can commit them to record changes made by a running process; audit those changes with a diff. Unroll the history of any container to reconstitute how it was assembled, step by step. You don't get commit messages because typically changes are snapshotted automatically by a build tool - instead you get the exact unix command which caused the change, as well as date etc. This means you can point to any container, ask "what's in there?", and get a meaningful answer. In theory that would be true if 100% of all code deployed used rpms or debs. In practice that never happens because developers never package everything that way.
You can branch off of any intermediary image. This branching mechanism is used by the build tool as a caching mechanism: if you re-build an image which runs "apt-get install", it will default to re-using the result of the previous run. Uploading and downloading of containers takes advantage of versioning, so that you only transfer missing versions (similarly to git push and pull), and only store each verion on disk once with copy-on-write.
A Dockerfile is a convenience for developers to specify exactly how to assemble a container from their source, independently of the platform. Each step of the Dockerfile is committed, and benefits from the aforementioned benefits.
Customization is a special case of assembly: just use a pre-existing container as a base, and assemble more stuff on top.
All of this can be tracked, managed and automated as described above.
> A deployment tool that did that would become very popular.