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
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.
The short answer to this is you don't, or at least you really shouldn't.
Yes, there are some container runtimes that allow you to change the default namespace, specifically those from RedHat. However, RedHat now regrets this functionality and discourages customers from using it. Docker has also refused to support this.
The reason this is so problematic is because is results in an ambiguous namespace of images. The same command run on two different machines could pull different images depending on what registry they are configured to use. Since compose files, helm templates, and other ways of running containers are shared between machines, this actually introduces a security vulnerability.
An attacker could squat on well known image names in registries other than Docker Hub with the hopes that a user may change their default configuration and accidentally run their image instead of the one from Hub. It would be trivial to create a fork of a tool like Jenkins, push the image to other registries, but with some code that sends all the credentials loaded into Jenkins out to an attacker server. We've even seen this causing security vulnerability reports this year for other package managers like PyPI, NPM, and RubyGems.
Instead, the direction of container runtimes like containerd is to make all image names fully qualified, removing the Docker Hub automatic expansion (tooling on top of containerd like Docker still apply the default expansion, so I doubt this is going away any time soon, if ever).
Docker does allow you to define registry mirrors for Docker Hub that it will query first before querying Hub, however this assumes everything is still within the same namespace and the mirror is just a copy of upstream images, not a different namespace of images. The TL;DR on how to set that up is the following in the /etc/docker/daemon.json and then systemctl reload docker:
{
"registry-mirrors": ["https://<my-docker-mirror-host>"]
}
For most, this is a non-issue (this issue to me is the docker engine doesn't have an option to mirror non-Hub registries). The image name is defined in a configuration file, or a script, and so typing it once in that file is easy enough. And with tooling like compose files and Helm templates, the registry can be turned into a variable to allow organizations to explicitly pull images for their deploy from a configurable registry name.
if you are using the fedora distro, you can change the file
/etc/containers/registries.conf
Adding domain docker.io
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
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.
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>"
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.
Didn't see the answer for MacOS, so want to add here:
2 Method as below:
Option 1 (Through Docker Desktop GUI):
Preference -> Docker Engine -> Edit file -> Apply and Restart
Option 2:
Directly edit the file ~/.docker/daemon.json
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?
I used the following command: docker pull balenalib/beaglebone-black:latest
I am now trying to find the page for this image on Docker Hub. I search balenalib/beaglebone-black:latest and thousands of results come up, but seemingly not the one I typed in.
I finally found it here by manipulating the URL directly.
Is there a better way to do this? Can I get to that URL by using a command from terminal?
For Docker's registry's web fronted (https://hub.docker.com), there are two primary 'views':
Users|Organizations:
e.g. https://hub.docker.com/u/balenalib
NB "hub.docker.com/u/"
Users'|Organizations' Images
e.g. https://hub.docker.com/r/balenalib/beaglebone-black
NB "hub.docker.com/r/"
In the case of Docker's registry, the docker pull includes an implicit|optional docker.io/ prefix as it defaults to Docker's registry but there are other registries:
docker pull docker.io/balenalib/beaglebone-black:latest
So there's a form docker pull [registry]/[user]/[image]:[tag]
And, if you're using Linux and Chrome, you could browse to it on DockerHub using:
USER=balenalib # for example
IMAGE=beaglebone-black # for example
google-chrome https://hub.docker.com/r/${USER}/${IMAGE}
NB I find this a confusing use of similar terms, but a registry (such as Docker's) includes many repositories. In your example, using the Docker registry, balenalib/beaglebone-black is one repository in it.
We have been using locked version of the Minio image (RELEASE.2016-10-07T01-16-39Z), but now it seems to have been removed.
I'm getting this from Docker:
Pulling minio (minio/minio:RELEASE.2016-10-07T01-16-39Z)...
Pulling repository docker.io/minio/minio
ERROR: Tag RELEASE.2016-10-07T01-16-39Z not found in repository docker.io/minio/minio
I'm finding Docker hub hard to navigate. Where can I find a list of available versioned images, or a mirror to my exact image?
You can find the available tags for minio/minio on that repository's tag page.
If you have the image you want already downloaded on any of your systems, you can push it to Docker Hub yourself, then pull it onto your other systems. This has the benefit that you can control whether you delete that image (it's your account, not someone else's).
You can also use a private registry, if you want, which would prevent Docker from deleting the image from Docker Hub against your will for some reason. But that is extra work you may not wish to do (you would have to host the registry yourself, set it up, maintain it...)
We removed the docker version due to incompatibilities, from the recent releases it won't happen.
One can easily build docker images through docker build command.
What I'm wondering is the t flag that you can give when building the image. For example:
$ docker build -t ouruser/sinatra:v2 .
According to documentation, the t flag is for tagging and naming purposes. Name is the part before ':', and tag is the part after it. So in our example, the name is ouruser/sinatra, and the tag is v2.
I thought this would be the image name and tag. But apparently, the name is actually some repository name? Why do I think it is? Well, because if you would after this list the images with command:
docker images
You would get a listing like this:
REPOSITORY TAG IMAGE ID CREATED SIZE
ouruser/sinatra latest 5db5f8471261 11 hours ago 446.7 M
Bang! Major shock! You thought you were creating an image with name, and instead, you specified some repository! Related to this, I have some questions:
Where is this repository located?
Can I name the image without creating a repository?
Where and how is this repository used, or could be used?
Where can I find more information about this repository? I only found this, and it doesn't tell much to be honest: docker build docs
Why is it common to use names that consist of two parts like this: somename/someothername?
Thank you for your help!
I believe the confusion here is the word "repository." In Docker, a repository is any group of builds of an image with the same name, and potentially multiple tags. A "registry" server, like hub.docker.com or your own private registry, holds multiple repositories, e.g. the redis repository on the public registry. That one repository has multiple tags for different versions of the build.
So with that background, to answer your questions:
ouruser/sinatra is located on your local Docker host until you do a docker push
No, the repository and the tag is the name of the image.
While local on your system, you can use this image locally. Once you push it up to a registry, you can then pull it down to any other Docker host that has access to that registry. And if you do a docker save you can save that image for a docker load on another host.
I'm sure there is documentation covering this somewhere on docs.docker.com, but I learned from a class.
The username/imagebase format came about to support pushing to your own namespace in hub.docker.com. Without that, whoever makes the first "Redis" image calls it "redis" while the next person makes their own repository called "redis-improved", and we quickly get into a jumble of confusing names where it's not clear who made what and what is a reputable image. That naming isn't required for images you make locally, but is still encouraged since images you pull from hub.docker.com may lack a username if they are maintained by Docker themselves. Without your username, you won't know which images you pulled down and which you built yourself.
I am new to docker and just going through the online links to understand how it works. However I am not getting much clarity on Docker Registry and Docker Index. I get that part that your docker image will be there on registry and client uses pull command to daemon which in turn get the image from registry. But I also read that you can get and image from Index as well then what is the difference between these two?
Thank you.
I think Where are Docker images stored? gives a good explanation:
An index manages user accounts, permissions, search, tagging, and all that nice stuff that's in the public web interface.
A registry stores and serves up the actual image assets, and it delegates authentication to the index.
When you run docker search, it's searching the index, not the registry. In fact, it might be searching multiple registries that the index is aware of.
When you run docker push or docker pull, the index determines if you are allowed to access or modify the image, but the registry is the piece that stores it or sends it down the wire to you after the index approves the operation. Also, the index figures out which registry that particular image lives in and forwards the request appropriately.
Beyond that, when you're working locally and running commands like docker images, you're interacting with something that is neither an index or a registry, but a little of both.
There is a slight difference, mostly because there were 2 API's developed, which were originally developed to be served by separate services.
https://github.com/docker/docker-registry implements the registry API, while the Docker Hub implements both.
I know of one open source implementation of the Index, which can be added to a docker-registry -
There is no difference. Both usually refers to Docker official image repository. You can also find it referred as Docker repository and Docker Hub. All of them usually refers to the same.
You also can find or set up an alternate repository and host there images, but then you would refer that repository as your repository or a particular name (e.g.: totum repository).
I'm not sure about Docker Registry. But a docker registry is a service that stores images, allowing you to pull and push them. distribution/registry is probably the most popular implementation. Docker Index is the former name of Docker Hub. There's also an index server, which is seemingly what's left from the registry v1 api if you extract the registry v2 api from it. Namely, searching for images. And apparently Docker Hub has both a docker registry and an index server.
More on it here.