Store images on Docker Hub

Store images on Docker Hub

So far you’ve learned how to use the command line to run Docker on your local host. You’ve learned how to pull down images to build containers from existing images and you’ve learned how to create your own images.

Next, you’re going to learn how to use the Docker Hub to simplify and enhance your Docker workflows.

The Docker Hub is a public registry maintained by Docker, Inc. It contains images you can download and use to build containers. It also provides authentication, work group structure, workflow tools like webhooks and build triggers, and privacy tools like private repositories for storing images you don’t want to share publicly.

Docker commands and Docker Hub

Docker itself provides access to Docker Hub services via the docker search, pull, login, and push commands. This page will show you how these commands work.

Account creation and login

Before you try an Engine CLI command, if you haven’t already, create a Docker ID. You can do this through Docker Hub. Once you have a Docker ID, log into your account from the Engine CLI:

$ docker login

The login command stores your Docker ID authentication credentials in the $HOME/.docker/config.json (Bash notation). For Windows cmd users the notation for this file is %HOME%\.docker\config.json ; for PowerShell users the notation is $env:Home\.docker\config.json.

Once you have logged in from the command line, you can commit and push Engine subcommands to interact with your repos on Docker Hub.

Searching for images

You can search the Docker Hub registry via its search interface or by using the command line interface. Searching can find images by image name, user name, or description:

$ docker search centos
NAME           DESCRIPTION                                     STARS     OFFICIAL   AUTOMATED
centos         The official build of CentOS                    1223      [OK]
tianon/centos  CentOS 5 and 6, created using rinse instea...   33
...

There you can see two example results: centos and tianon/centos. The second result shows that it comes from the public repository of a user, named tianon/, while the first result, centos, doesn’t explicitly list a repository which means that it comes from the trusted top-level namespace for Official Repositories. The / character separates a user’s repository from the image name.

Once you’ve found the image you want, you can download it with docker pull <imagename>:

$ docker pull centos
Using default tag: latest
latest: Pulling from library/centos
f1b10cd84249: Pull complete
c852f6d61e65: Pull complete
7322fbe74aa5: Pull complete
Digest: sha256:90305c9112250c7e3746425477f1c4ef112b03b4abe78c612e092037bfecc3b7
Status: Downloaded newer image for centos:latest

You now have an image from which you can run containers.

Specific Versions or Latest

Using docker pull centos is equivalent to using docker pull centos:latest. To pull an image that is not the default latest image you can be more precise with the image that you want.

For example, to pull version 5 of centos use docker pull centos:centos5. In this example, centos5 is the tag labeling an image in the centos repository for a version of centos.

To find a list of tags pointing to currently available versions of a repository see the Docker Hub registry.

Contributing to Docker Hub

Anyone can pull public images from the Docker Hub registry, but if you would like to share your own images, then you must register first.

Pushing a repository to Docker Hub

In order to push a repository to its registry, you need to have named an image or committed your container to a named image as we saw here.

Now you can push this repository to the registry designated by its name or tag.

$ docker push yourname/newimage

The image will then be uploaded and available for use by your team-mates and/or the community.

Features of Docker Hub

Let’s take a closer look at some of the features of Docker Hub. You can find more information here.

• Private repositories
• Organizations and teams
• Automated Builds
• Webhooks

Private repositories

Sometimes you have images you don’t want to make public and share with everyone. So Docker Hub allows you to have private repositories. You can sign up for a plan here.

Organizations and teams

One of the useful aspects of private repositories is that you can share them only with members of your organization or team. Docker Hub lets you create organizations where you can collaborate with your colleagues and manage private repositories. You can learn how to create and manage an organization here.

Automated Builds

Automated Builds automate the building and updating of images from GitHub or Bitbucket, directly on Docker Hub. It works by adding a commit hook to your selected GitHub or Bitbucket repository, triggering a build and update when you push a commit.

To setup an Automated Build

1. Create a Docker Hub account and login.
2. Link your GitHub or Bitbucket account on the “Linked Accounts & Services” page.
3. Select “Create Automated Build” from the “Create” dropdown menu
4. Pick a GitHub or Bitbucket project that has a Dockerfile that you want to build.
5. Pick the branch you want to build (the default is the master branch).
6. Give the Automated Build a name.
7. Assign an optional Docker tag to the Build.
8. Specify where the Dockerfile is located. The default is /.

Once the Automated Build is configured it will automatically trigger a build and, in a few minutes, you should see your new Automated Build on the Docker Hub Registry. It will stay in sync with your GitHub and Bitbucket repository until you deactivate the Automated Build.

To check the output and status of your Automated Build repositories, click on a repository name within the “Your Repositories” page. Automated Builds are indicated by a check-mark icon next to the repository name. Within the repository details page, you may click on the “Build Details” tab to view the status and output of all builds triggered by the Docker Hub.

Once you’ve created an Automated Build you can deactivate or delete it. You cannot, however, push to an Automated Build with the docker push command. You can only manage it by committing code to your GitHub or Bitbucket repository.

You can create multiple Automated Builds per repository and configure them to point to specific Dockerfile’s or Git branches.

Build triggers

Automated Builds can also be triggered via a URL on Docker Hub. This allows you to rebuild an Automated build image on demand.

Webhooks

Webhooks are attached to your repositories and allow you to trigger an event when an image or updated image is pushed to the repository. With a webhook you can specify a target URL and a JSON payload that will be delivered when the image is pushed.

See the Docker Hub documentation for more information on webhooks

Next steps

Go and use Docker!