Docker Hub

Docker Hub is a Docker Registry offered by Docker Inc. It allows unlimited storage of public images, and paid plans to host your private images. A public image may be accessed by others, which is precisely what you want when you make your software widely available - less for internal enterprise software.

To publish images on Docker Hub, you need to create an account. I’m going to create one. For this, I head to https://hub.docker.com/ and click the Sign Up link. The Docker ID I select will be the prefix of images I publish to the Docker Hub.

When creating your account, make sure you select the right ID since it will be part of your images’ names. Suppose your ID name is short-name, your images should be tagged:

For this course, I created the learnbook account, and I want to publish the webserver image I created earlier. It’s as simple as naming it correctly and pushing it to the Registry. I need to name it learnbook/webserver, and there are two ways to do this.

The first is to run the docker build command again using the correct name. This is a good option when you’re using it from the start, but if I do this now it will result in two separate images on my disk, the same contents but two different names and IDs which is not a good idea.

My second option is much better; use the docker tag command. A Docker image can have several names as needed, and they can be added to an already existing image thanks to the docker tag command. The docker tag doesn’t duplicate the image contrary to running docker build again.

The docker tag command accepts two arguments; first, the name of an existing image, and second, the name you want to add to that image.

I now have a single Docker image known by my machine under two names: webserver and short_name/webserver. When I run the docker image ls command, it will appear as two separate lines:

Note that the image ID is the same for both lines, which means there really is just one image on my machine, known under two different names.

Now that my image is named correctly, I can publish it to the Docker hub. It’s just a matter of running two commands:

The docker login command asks for my Docker Hub credentials interactively, but I could have just as well provided them as arguments to the command.

The docker push command is smart enough to push only the bits that differ from the base nginx image I used since it is already stored in the Docker Hub, as the output shows:

The push refers to repository [docker.io/learnbook/webserver]
0f83d7865e1e: Pushed
6b5e2ed60418: Mounted from library/nginx
92c15149e23b: Mounted from library/nginx
0a07e81f5da3: Mounted from library/nginx
latest: digest: sha256:e8597...1ae0b1efb1 size: 1155

Run the above commands in the given terminal to verify the results. Keep in mind to replace the learnbook ID in the above commands with your own docker ID. The docker ID can be obtained by simply making your account as explained above. Your output might be different from the above-mentioned one.

That’s it! The Docker Hub now hosts the image for everyone to see and run it.

Everyone can see the image because it is public. In case you don’t want to share it with the whole world, you can set it as private.

In the next lesson, let’s run the image we just published.