2.1. Registry and Docker Hub

So far, we only built and ran the Docker images locally on our computers, but what if we want to integrate them into a CI/CD pipeline or even only distribute the built images? Similar to a Maven artifact repo, where the built JARs, WARs, and EARs get deployed to distribute later, there is the concept of a Docker registry.

In this lab we’re going to learn:

  • Docker Hub platform
  • Pull and push images from and to the registry
  • Create automated docker builds on Docker Hub

Docker Hub

Most of the images and base images you ran in the previous labs were downloaded from Docker Hub, when not already present on your computer.

Docker Hub is an online Docker registry, repository management, and build platform. It consists of public and private repositories. Docker Hub integrates with various online services such as GitHub or GitLab.

Publicly available images can be pulled without logging into the platform.

The following command pulls the nginx image to your local machine

docker pull nginx

Using default tag: latest
latest: Pulling from library/nginx
f17d81b4b692: Pull complete
d5c237920c39: Pull complete
a381f92f36de: Pull complete
Digest: sha256:4ddaf6043a77aa145ce043d4c662e3768556421d6c0a65d303e89977ad3c9636
Status: Downloaded newer image for nginx:latest

Run the following command to verify whether the image is now locally available or not.

docker images

REPOSITORY                                               TAG                 IMAGE ID            CREATED             SIZE
nginx                                                    latest              dbfc48660aeb        4 hours ago         109MB

docker run or docker build does a docker pull implicitly when an image is not yet locally available.

(Optional) Create a Docker Hub account

You can create your personal Docker Account for later use in this task. If you just wan’t to see how uploading an image works you can skip this task. Now it’s time to prepare for pushing a docker image to a Docker Hub repository.

  • Create a Docker Hub account, if you don’t already have one: https://hub.docker.com/
  • Create a new public repository: use the Create Repository button after logging in.
  • Check the repository info, the newly created repository is empty.

Log in to Docker Hub with your account:

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: <username>
Password: <password>
WARNING! Your password will be stored unencrypted in /home/home/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded

Usage of an anonymous Container registry

There are many container registries out there. For our lab tasks we can also use a temporary registry like https://ttl.sh/ (altough it should not be used for confidential data.)

Push your first image

If you have created a Docker Hub account you can upload myfirstimage there:

But first we need to tag the image with the same name as the repository we’ve created previously:

docker tag myfirstimage <docker-user>/<docker-repo>
docker push <docker-user>/<docker-repo>

The push refers to repository docker.io/<docker-user>/<docker-repo>
213d31159bea: Pushed
9f9cacfd69bf: Pushed
a1950e3866f0: Mounted from library/php
2dc96af1a4a5: Mounted from library/php
8cb5b8d4756a: Mounted from library/php
bcc4727d0912: Mounted from library/php
59e338bee70e: Mounted from library/php
369e6fd590f3: Mounted from library/php
1805144065e1: Mounted from library/php
b6311cdc5fb6: Mounted from library/php
e30181a94bbf: Mounted from library/php
481da43a1302: Mounted from library/php
a4ace4ed0385: Mounted from library/php
fd29e0f8792a: Mounted from library/php
687dad24bb36: Mounted from library/php
237472299760: Mounted from library/php
latest: digest: sha256:604c7893ff67fab19fddcaaf89935f9bd252a8711e1d42ab3c8c837144b57eee size: 3659

If you don’t have a Docker account you can upload myfirstimage to https://ttl.sh/ like this:

docker tag myfirstimage ttl.sh/yourname/myfirstimage
docker push ttl.sh/yourname/myfirstimage

Without further options this image will stay on the registry for 24hours.

Tagging images

Tagging images allows us to keep track of different versions without the need of remembering the image ID, e.g. ca751384b926. This said, a tag is a pointer to a specific image ID.

docker images

REPOSITORY                                               TAG                 IMAGE ID            CREATED             SIZE
myfirstimage                                             latest              ca751384b926        About an hour ago   368MB
songlaa/container-training                               1                   ca751384b926        About an hour ago   368MB
songlaa/container-training                               latest              ca751384b926        About an hour ago   368MB
nginx                                                    latest              dbfc48660aeb        5 hours ago         109MB
...

Tagging an image by ID:

docker tag <image-id> songlaa/container-training:<tag>

Tagging an image by name:

docker tag myfirstimage songlaa/container-training:<tag>

Tagging an image by name and tag:

docker tag myfirstimage:1 songlaa/container-training:<tag>

Tagging an image for a private registry:

docker tag <image> myregistryhost:5000/songlaa/container-training:<tag>

Docker Enterprise

Docker has its own enterprise features, which are available for Enterprises at https://www.docker.com/products/docker-enterprise .

Docker Hub alternatives

There are a couple of other public registries available, such as https://quay.io/ for example.

Private registries

A docker registry can be deployed on premises or in your Cloud subscriptions as well. Most of the available artifact repository applications such as Nexus and Artifactory are able to manage Docker images as well.

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