All-Things-Docker-and-Kubernetes
Lab 009: Tagging Images
- Pre-requisites
- Introduction
- Example 1: Single Tag
- Example 2: Dockerhub Username and Image Name
- Example 3: Multiple Tags
- Example 4: Versions
- Cleanup
Pre-requisites
Introduction
In this lab, we’ll get to see how to use tagging for docker images. It is recommended to provide your images with tags and practice it early on since it’ll be helpful when identifying versions and features of the images.
Example 1: Single Tag
Create the File
Create dockerfile-1. Here we’re using CentOS version 7 as the base image and we’re installing Java on top of it.
FROM centos:7
RUN yum -y install wget
RUN yum -y install unzip
RUN yum -y install java-1.8.0-openjdk
RUN yum clean all
ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/
RUN export JAVA_HOME
Build an Image with a Single Tag
Use the “-f” flag to specify the dockerfile-1.
$ docker build -t "centos-java-1" -f dockerfile-1 .
Notice that we have two images created. Since our dockerfile-1 uses a CentOS:7 image, it pulls the official image from the dockerhub repository
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos-java-1 latest f4da659e7493 25 seconds ago 939MB
centos 7 eeb6ee3f44bd 9 months ago 204MB
Example 2: Dockerhub Username and Image Name
Create an Account in Dockerhub
For this example, we would need to create a free account in Dockerhub. You should also be able to link your Github account to it.
Once you have your account setup, create a repository. I’m using “centos-java-1” as my repository name.
Back in your terminal, login to dockerhub. Enter your username and password.
$ sudo 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: edenjose
Password:
Using Docker Tag
We currently have these two images.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos-java-1 latest f4da659e7493 16 minutes ago 939MB
centos 7 eeb6ee3f44bd 9 months ago 204MB
We want to tag it with another tag and the username for our docker registry using the format below.
$ sudo docker tag <image ID> <username/repo-name>:latest
$ docker tag f4d edenjose/centos-java-1:v1
When we check our images, we now see three images. There’s actually just two images; the first two are pointing to the same image ID as seen below.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
edenjose/centos-java-1 v1 f4da659e7493 20 minutes ago 939MB
centos-java-1 latest f4da659e7493 20 minutes ago 939MB
centos 7 eeb6ee3f44bd 9 months ago 204MB
Pushing the Image to the Registry
Now that it’s prepped-up, we’re ready to push it to our dockerhub repo.
sudo docker push <username/repo-name>
$ sudo docker push edenjose/centos-java-1:v1
Checking in Dockerhub,
Example 3: Multiple Tags
Let’s build an image from the same dockerfile-1 in Example 1. These time we’ll use “-t” for every tags we give to the image.
$ docker build -f dockerfile-1 \
-t project-centos-java:projectX \
-t feature-centos-java:v1.a2 \
-t devops-centos-java:devops-team.v12.0 .
We can see that five tags have been created for the same image ID.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
edenjose/centos-java-1 v1 f4da659e7493 35 minutes ago 939MB
centos-java-1 latest f4da659e7493 35 minutes ago 939MB
devops-centos-java devops-team.v12.0 f4da659e7493 35 minutes ago 939MB
feature-centos-java v1.a2 f4da659e7493 35 minutes ago 939MB
project-centos-java projectX f4da659e7493 35 minutes ago 939MB
centos 7 eeb6ee3f44bd 9 months ago 204MB
Example 4: Versions
Remove the images created from the previous examples.
$ docker image prune --all --force
Create the File
Create dockerfile-2. Here we’re using Ubuntu version 16.04 as the base image. We’re also creating a demo directory with a file named message inside.
When the container is ran, it will print out the message in stdout by using the “/bin/bash” command.
FROM ubuntu:16.04
RUN mkdir -p /demo && \
echo "Version 1" > /demo/message
CMD ["/bin/cat", "/demo/message"]
Build the Image and Run the Container
Here we’re not specifying a tag for the “lab08” image ID. Docker will automatically give the image a “latest” tag.
$ docker build -f dockerfile-2 -t lab08 .
As expected, we’ll see two images created. The first one is the official Ubuntu image pulled down from the Dockerhub repository and is used as the base image for our “lab08” image.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
lab08 latest 29b1931e8be7 9 seconds ago 135MB
ubuntu 16.04 b6f507652425 9 months ago 135MB
To add another tag to the lab08 image,
$ docker tag lab08:latest lab08:v1
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
lab08 latest 29b1931e8be7 43 seconds ago 135MB
lab08 v1 29b1931e8be7 43 seconds ago 135MB
ubuntu 16.04 b6f507652425 9 months ago 135MB
If we run a container from the “lab08” image without specifying the tag, it will automatically use the one tagged “latest”. When we run the container, it should return the “Version 1” as we’ve specified in the dockerfile-2.
$ docker run lab08
Version 1
Modify the Dockerfile and Build another Image
Edit the dockerfile-2.
FROM ubuntu:16.04
RUN mkdir -p /demo && \
echo "Version 2" > /demo/message
CMD ["/bin/cat", "/demo/message"]
Build the image and add a tag “v2”.
$ docker build -f dockerfile-2 -t lab08:v2 .
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
lab08 v2 768ec6c8d404 7 seconds ago 135MB
lab08 latest 29b1931e8be7 5 minutes ago 135MB
lab08 v1 29b1931e8be7 5 minutes ago 135MB
ubuntu 16.04 b6f507652425 9 months ago 135MB
Now run containers from the images tagged with “latest”, “v1” and “v2”.
$ docker run lab08
Version 1
$ docker run lab08:v1
Version 1
$ docker run lab08:v2
Version 2
As expected, the “latest” and “v1” were built from the dockerfile with “Version 1” as the message. The message has been “baked” onto the image so that when the dockerfile was modified, the two images tagged with “latest” and “v1” were not affected.
Cleanup
When you’re done with the lab, you can stop all running containers by running the command below.
$ docker stop $(docker ps)
Once all containers have “Exited” status, remove them.
$ docker ps -a
$ docker container prune -f
Finally, remove all images.
$ docker image prune -af