How to Load a Docker Image: Step-by-Step Guide

Docker is essential for managing and deploying apps in containerized environments. One of Docker's core functions is working with images, which are standalone, portable, and executable software packages. The 'docker image load' command is a crucial tool for loading Docker images from a tarball into the local Docker image store. This is very useful when you need to transfer Docker images between systems or contexts without relying on a Docker registry.

Understanding some basic terminologies

• Docker Image: a read-only template that can be created for Docker containers. The runtime, libraries, environment variables, application code, and configurations needed to operate an application are all included.
• Docker Container: An instance of a Docker image running as a separate process. Containers are isolated from each other and from the host system.
• Tarball: A compressed archive file (usually with a .tar, .tar.gz, or .tgz extension) that can bundle multiple files into a single file. In the context of Docker, it often contains the layers and metadata of a Docker image.
• Docker Image Store: The local storage area where Docker images are kept on your system. These images are used to create and run containers.

Step-by-Step Process of Using 'docker image load'

So let's continue step-by-step guide of using 'docker image load' command.

Step 1: Export the Docker Image as tarball (Optional)

• Before using 'docker image load' command, you need a tarball of docker image. If you already have, then simply ignore this step and proceed to the next one.
• To export the docker image as tarball, we need to use 'docker save'. The command is shown below:

docker save -o my-image.tar img-name

The above command creates a tarball named 'my-image.tar' of the 'img-name' docker image.

Step 2: Load the Docker Image

• Once the tarball is present, you can load it into your local Docker image store with the 'docker image load' command.

docker image load -i my-image.tar

The above command will load the docker image present in 'my-image.tar'.

Step 3: Verify the Loaded Image

• Once the image is loaded, you can verify by using 'docker images' command. It will list all the available docker images.

docker images

The command will list images along with its tags, image ID, and size.

Conclusion

The 'docker image load' command is an crucial tool for managing Docker images, especially in scenarios where you need to transfer images between different environments without using a Docker registry. You can seamlessly and successfully operate within your containerized apps by knowing how to utilize this command efficiently.

What is the difference between 'docker load' and 'docker import'?

'docker load' loads a Docker image (along with its tags, layers, and history) from a tarball created by 'docker save'. Whereas 'docker import', creates a new image from a tarball but doesn’t preserve the image’s history or tags. 'docker import' is often used for importing filesystem snapshots.

Can I use 'docker image load' to load images directly from a remote location?

No, 'docker image' load needs the tarball to be present locally. You need to download the tarball first before loading it.

Is it possible to load multiple images at once using 'docker image load'?

Yes, if the tarball contains multiple images (e.g., created by saving a multi-image repository), 'docker image load' will load all the images within the tarball.

What happens if the image already exists in the local image store?

If the image already exists, 'docker image load' will either overwrite the existing image or keep both versions if they have different tags. It depends on the image’s tag and ID.

Can I load an image into a specific repository or with a different tag?

No, 'docker image load' loads the image with the tags that were saved in the tarball. To change the repository or tag, you would need to use the 'docker tag' command after loading the image.