Docker image push over SSH (distributed)

Question

TL;DR Basically, I am looking for this:

docker push myimage ssh://myvps01.vpsprovider.net/

I am failing to grasp the rationale behind whole Docker Hub / Registry thing. I know I can run a private registry, but for that I have to set up the infrastructure of actually running a server.

I took a sneak peek inside the inner workings of Docker (well, the filesystem at least), and it looks like Docker image layers are just a bunch of tarballs, more or less, with some elaborate file naming. I naïvely think it would not be impossible to whip up a simple Python script to do distributed push/pull, but of course I did not try, so that is why I am asking this question.

Are there any technical reasons why Docker could not just do distributed (server-less) push/pull, like Git or Mercurial?

I think this would be a tremendous help, since I could just push the images that I built on my laptop right onto the app servers, instead of first pushing to a repo server somewhere and then pulling from the app servers. Or maybe I have just misunderstood the concept and the Registry is a really essential feature that I absolutely need?

EDIT Some context that hopefully explains why I want this, consider the following scenario:

• Development, testing done on my laptop (OSX, running Docker machine, using docker-compose for defining services and dependencies)
• Deploy to a live environment by means of a script (self-written, bash, few dependencies on dev machine, basically just Docker machine)
• Deploy to a new VPS with very few dependencies except SSH access and Docker daemon.
• No "permanent" services running anywhere, i.e. I specifically don't want to host a permanently running registry (especially not accessible to all the VPS instances, though that could probably be solved with some clever SSH tunneling)

The current best solution is to use Docker machine to point to the VPS server and rebuild it, but it slows down deployment as I have to build the container from source each time.

Answer 1

If you want to push docker images to a given host, there is already everything in Docker to allow this. The following example shows how to push a docker image through ssh:

docker save <my_image> | ssh -C [email protected] docker load

• docker save will produce a tar archive of one of your docker images (including its layers)
• -C is for ssh to compress the data stream
• docker load creates a docker image from a tar archive

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Note that the combination of a docker registry + docker pull command has the advantage of only downloading missing layers. So if you frequently update a docker image (adding new layers, or modifying a few last layers) then the docker pull command would generate less network traffic than pushing complete docker images through ssh.