How to use docker image push command to upload images

Introduction

In this lab, you will learn how to upload your Docker images to a registry using the docker image push command. This process is essential for sharing your custom images with others or deploying them to different environments.

You will begin by committing changes made within a running container to create a new image. Then, you will learn how to tag this image appropriately for a specific registry, which is a crucial step before pushing. Finally, you will practice pushing the tagged image to the registry, including how to push all tags associated with an image.

Commit a container to a new image

In this step, you will learn how to commit changes made inside a running container to a new Docker image. This is useful when you want to save the state of a container after making modifications, such as installing software or configuring files.

First, let's run a simple Ubuntu container. We will use the ubuntu image. Since we will make changes inside the container, we need to run it interactively with a pseudo-TTY.

docker run -it ubuntu

You should now be inside the Ubuntu container's shell. Let's make a simple change, like installing the curl package.

apt-get update
apt-get install -y curl

After the installation is complete, exit the container's shell by typing exit.

exit

Now that you have exited the container, the changes you made (installing curl) are still present in that specific container instance. To save these changes as a new image, you need to commit the container.

First, find the container ID of the container you just exited. You can use the docker ps -a command to list all containers, including those that have exited.

docker ps -a

Look for the container that was created from the ubuntu image and note its CONTAINER ID.

Now, use the docker commit command to create a new image from this container. The basic syntax is docker commit [OPTIONS] CONTAINER [REPOSITORY[:TAG]]. We will commit the container and give the new image a name and tag. Replace <CONTAINER_ID> with the actual ID you found.

docker commit < CONTAINER_ID > my-ubuntu-with-curl:v1

This command creates a new image named my-ubuntu-with-curl with the tag v1. You can verify that the new image has been created by listing your local images.

docker images

You should see my-ubuntu-with-curl in the list of images. This new image now includes the curl package that you installed in the container.

Tag the image for a specific registry

In this step, you will learn how to tag a Docker image so that it can be pushed to a specific container registry. When you push an image to a registry, the tag is used to identify the image within that registry. The standard format for tagging an image for a registry is [registry-hostname[:port]]/repository[:tag].

In the previous step, you created an image named my-ubuntu-with-curl with the tag v1. Now, let's tag this image for a hypothetical registry. For demonstration purposes, we will use localhost:5000 as our registry address.

You can use the docker tag command to create a new tag for an existing image. The basic syntax is docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG].

Let's tag the my-ubuntu-with-curl:v1 image for our hypothetical registry.

docker tag my-ubuntu-with-curl:v1 localhost:5000/my-ubuntu-with-curl:v1

This command creates a new tag localhost:5000/my-ubuntu-with-curl:v1 that points to the same image as my-ubuntu-with-curl:v1.

You can verify that the new tag has been added by listing your local images again.

docker images

You should now see an entry for localhost:5000/my-ubuntu-with-curl with the tag v1. This indicates that the image is now tagged and ready to be pushed to the registry at localhost:5000.

Push the tagged image to the registry

In this step, you will learn how to push a tagged Docker image to a container registry. Pushing an image makes it available for others to pull and use.

Before you can push an image to a local registry, you need to have a registry running. For this lab, we will run a temporary local registry container.

First, pull the registry image.

docker pull registry:2

Now, run the registry container. We will map port 5000 on the host to port 5000 on the container.

docker run -d -p 5000:5000 --name local-registry registry:2

This command starts a detached container named local-registry running the Docker registry.

In the previous step, you tagged the image my-ubuntu-with-curl:v1 with localhost:5000/my-ubuntu-with-curl:v1. This tag includes the address of our local registry (localhost:5000).

Now, you can push this tagged image to the local registry using the docker push command. The syntax is docker push NAME[:TAG].

docker push localhost:5000/my-ubuntu-with-curl:v1

You should see output indicating the progress of the push operation, including the layers being pushed.

After the push is complete, the image my-ubuntu-with-curl:v1 is now stored in your local registry at localhost:5000.

Push all tags of an image

In this step, you will learn how to push all tags associated with a specific image to a container registry. Sometimes, you might have multiple tags pointing to the same image (e.g., latest, v1.0, stable). You can push all of these tags with a single command.

In the previous steps, you created an image my-ubuntu-with-curl and tagged it as v1 and localhost:5000/my-ubuntu-with-curl:v1. Let's add another tag to this image. We will tag it as latest for our local registry.

Use the docker tag command again to add the latest tag.

docker tag my-ubuntu-with-curl:v1 localhost:5000/my-ubuntu-with-curl:latest

Now, list your images to see the new tag.

docker images

You should now see localhost:5000/my-ubuntu-with-curl with both v1 and latest tags, both pointing to the same image ID.

To push all tags of this image to the local registry, you can use the docker push command with the repository name without specifying a tag.

docker push localhost:5000/my-ubuntu-with-curl

Docker will identify all tags associated with the localhost:5000/my-ubuntu-with-curl repository and push each one to the registry. You will see output indicating the push progress for both the v1 and latest tags.

After the push is complete, both versions of your image (v1 and latest) are available in your local registry.

Summary

In this lab, you learned how to commit changes made inside a running Docker container to a new image. This process involves running a container, making modifications within it (such as installing software), exiting the container, identifying the container's ID, and then using the docker commit command to create a new image based on the container's state. You also learned how to assign a name and tag to the newly created image and verify its existence using docker images.