[docker] How to change the default docker registry from docker.io to my private registry?

By default, if I issue command:

sudo docker pull ruby:2.2.1

it will pull from the docker.io offical site by default.

Pulling repository docker.io/library/ruby

How do I change it to my private registry. That means if I issue

sudo docker pull ruby:2.2.1

it will pull from my own private registry, the output is something like:

Pulling repository my_private.registry:port/library/ruby

It seems it won't be supported due to the fragmentation it would create within the community (i.e. two users would get different images pulling ubuntu:latest). You simply have to add the host in front of the image name. See this github issue to join the discussion.

(Note, this is not intended as an opinionated comment, just a very short summary of the discussion that can be followed in the mentioned github issue.)

I tried to add the following options in the /etc/docker/daemon.json. (I used CentOS7)

"add-registry": ["192.168.100.100:5001"],
"block-registry": ["docker.io"],

after that, restarted docker daemon. And it's working without docker.io. I hope this someone will be helpful.

Haven't tried, but maybe hijacking the DNS resolution process by adding a line in /etc/hosts for hub.docker.com or something similar (docker.io?) could work?

Earlier this could be achieved using DOCKER_OPTS in the /etc/default/docker config file which worked on Ubuntu 14:04 and had some issues on Ubuntu 15:04. Not sure if this has been fixed.

The below line needs to go into the file /etc/default/docker on the host which runs the docker daemon. The change points to the private registry is installed in your local network. Note: you would require to restart the docker service followed with this change.

DOCKER_OPTS="--insecure-registry <priv registry hostname/ip>:<port>"

UPDATE: Following your comment, it is not currently possible to change the default registry, see this issue for more info.

You should be able to do this, substituting the host and port to your own:

docker pull localhost:5000/registry-demo

If the server is remote/has auth you may need to log into the server with:

docker login https://<YOUR-DOMAIN>:8080

Then running:

docker pull <YOUR-DOMAIN>:8080/test-image

There is the use case of a mirror of Docker Hub (such as Artifactory or a custom one), which I haven't seen mentioned here. This is one of the most valid cases where changing the default registry is needed.

Luckily, Docker (at least version 19.03.3) allows you to set a mirror (tested in Docker CE). I don't know if this will work with additional images pushed to that mirror that aren't on Docker Hub, but I do know it will use the mirror instead. Docker documentation: https://docs.docker.com/registry/recipes/mirror/#configure-the-docker-daemon.

Essentially, you need to add "registry-mirrors": [] to the /etc/docker/daemon.json configuration file. So if you have a mirror hosted at https://my-docker-repo.my.company.com, your /etc/docker/daemon.json should contain:

{
  "registry-mirrors": ["https://my-docker-repo-mirror.my.company.com"]
}

Afterwards, restart the Docker daemon. Now if you do a docker pull postgres:12, Docker should fetch the image from the mirror instead of directly from Docker Hub. This is much better than prepending all images with my-docker-repo.my.company.com

It turns out this is actually possible, but not using the genuine Docker CE or EE version.

You can either use Red Hat's fork of docker with the '--add-registry' flag or you can build docker from source yourself with registry/config.go modified to use your own hard-coded default registry namespace/index.

Docker official position is explained in issue #11815 :

Issue 11815: Allow to specify default registries used in pull command

Resolution:

Like pointed out earlier (#11815), this would fragment the namespace, and hurt the community pretty badly, making dockerfiles no longer portable.

[the Maintainer] will close this for this reason.

Red Hat had a specific implementation that allowed it (see anwser, but it was refused by Docker upstream projet). It relied on --add-registry argument, which was set in /etc/containers/registries.conf on RHEL/CentOS 7.

EDIT:

Actually, Docker supports registry mirrors (also known as "Run a Registry as a pull-through cache"). https://docs.docker.com/registry/recipes/mirror/#configure-the-docker-daemon

if you are using the fedora distro, you can change the file

/etc/containers/registries.conf

Adding domain docker.io

I'm adding up to the original answer given by Guy which is still valid today (soon 2020).

Overriding the default docker registry, like you would do with maven, is actually not a good practice.

When using maven, you pull artifacts from Maven Central Repository through your local repository management system that will act as a proxy. These artifacts are plain, raw libs (jars) and it is quite unlikely that you will push jars with the same name.

On the other hand, docker images are fully operational, runnable, environments, and it makes total sens to pull an image from the Docker Hub, modify it and push this image in your local registry management system with the same name, because it is exactly what its name says it is, just in your enterprise context. In this case, the only distinction between the two images would precisely be its path!!

Therefore the need to set the following rule: the prefix of an image indicates its origin; by default if an image does not have a prefix, it is pulled from Docker Hub.