Pushing an image to the Docker registry

Sharing container images using the registry is performed via an image push. This process uploads the required image layers to the selected repository in a registry and makes it available for pull by other users that have access to a given repository. In the case of Docker Hub, which we will use for this demonstration, your repositories will be public, unless you have a paid plan.

Pushing images to Docker Hub requires authentication. If you haven't already registered at Docker Hub, please navigate to https://hub.docker.com/ and follow the instructions there. After registration, you will need your Docker ID and password in order to log in to the services using the docker login command:

PS C:\WINDOWS\system32> docker login 
Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.
Username: packtpubkubernetesonwindows
Password:
Login Succeeded

Throughout this book, we will be using the packtpubkubernetesonwindows Docker ID in order to demonstrate our examples. It is recommended that you create your own account to be able to fully follow the examples in this book. Follow these steps:

1. The first step is to create an image that can actually be pushed to the registry. We will use the following Dockerfile to create the image:

FROM mcr.microsoft.com/windows/servercore/iis:windowsservercore-1903

WORKDIR /inetpub/wwwroot
RUN powershell -NoProfile -Command ; \
    Remove-Item -Recurse .\* ; \
    New-Item -Path .\index.html -ItemType File ; \
    Add-Content -Path .\index.html -Value \"This is an IIS demonstration!\"

This Dockerfile creates an IIS web host image, which serves a minimalistic web page that displays This is an IIS demonstration!.

2. Save the Dockerfile in your current directory. To build it, issue the following docker build command:

docker build -t <dockerId>/iis-demo .

Bear in mind that you have to supply your Docker ID as part of the repository name in order to be able to push the image to Docker Hub.

3. After a successful build, you are ready to perform an image push to the registry. This can be performed with the docker push command:

docker push <dockerId>/iis-demo

The following screenshot shows the output of the preceding command:

Docker pushes the image as a set of layers, which also optimizes the push process if already known layers are being used. Also, note that in the case of Windows-based images, you will see a Skipped foreign layer message. The reason for this is that any layers that come from a registry other than Docker Hub, such as Microsoft Container Registry (MCR), will not be pushed to Docker Hub.

Now, you can also navigate to the Docker Hub web page and check your image details – for the example image, you can check it here: https://cloud.docker.com/repository/docker/packtpubkubernetesonwindows/iis-demo/. Any user that has access to your repository can now use the docker pull <dockerId>/iis-demo command in order to use your image.

You have successfully pushed your first image to Docker Hub! Now, let's take a look at pushing images to custom image registries.