How can you copy Docker images from one host to another without using a repository?

Copying Docker Images Without a Repository

We can copy Docker images from one host to another without using a repository. We do this by using the Docker save and load commands. This way, we export a Docker image to a tar file. Then we transfer that file to another host using secure copy protocols like SCP. After the tar file is on the other host, we can load the image back into Docker. This makes it easy to transfer images.

In this article, we will show the steps to copy Docker images between hosts without a repository. We will talk about how to save a Docker image to a tar file. We will also explain how to transfer it using SCP. After that, we will load the image from the tar file. Finally, we will verify that the transfer was successful. Here is what we will explore:

  • How to Save a Docker Image to a Tar File
  • How to Transfer Docker Images Using SCP
  • How to Load a Docker Image from a Tar File
  • How to Use Docker Save and Docker Load Commands
  • How to Verify the Docker Image Transfer
  • Frequently Asked Questions

For more info about Docker images and how they work, we suggest reading this article on what are Docker images and how do they work.

How to Save a Docker Image to a Tar File

We can save a Docker image to a tar file by using the docker save command. This command exports the image and its info into one tar archive. We can then transfer or store this archive easily.

Command Syntax

docker save -o <output_file>.tar <image_name>:<tag>

Example

If we want to save an image named my_app with the tag latest to a file called my_app_latest.tar, we use this command:

docker save -o my_app_latest.tar my_app:latest

Options

  • -o <output_file>.tar: This is the name of the tar file we want to create.
  • <image_name>:<tag>: This shows the name and tag of the Docker image we want to save.

Verifying Saved Image

To check if the image saved correctly, we can list the contents of the tar file:

tar -tf my_app_latest.tar

This command will show us the files in the tar archive. It helps us to ensure that the image has been saved right.

For more details on Docker images, we can read what are Docker images and how do they work.

How to Transfer Docker Images Using SCP

To move Docker images from one host to another with Secure Copy Protocol (SCP), we can follow these simple steps after saving the image to a tar file. Make sure we have SSH access to the destination host.

  1. Save the Docker image to a tar file: We use the docker save command to export the Docker image. We need to replace your_image_name and your_image_version with our specific image name and version.

    docker save -o your_image_name.tar your_image_name:your_image_version

  2. Transfer the tar file using SCP: We can use the SCP command to copy the tar file to the target host. Replace user, hostname, and path/to/destination with the right SSH user, the IP address or hostname of the target host, and the destination folder where we want to save the image.

    scp your_image_name.tar user@hostname:path/to/destination

  3. Load the Docker image on the destination host: After the file is transferred, we log into the destination host using SSH. Then we load the Docker image with the docker load command.

    docker load -i path/to/destination/your_image_name.tar

By doing these steps, we can easily transfer Docker images between hosts without a repository. For more on Docker images and how they work, check out What are Docker Images and How Do They Work?.

How to Load a Docker Image from a Tar File

To load a Docker image from a tar file, we can use the docker load command. This command takes an image from a tar file and puts it into our local Docker image repository.

Steps to Load a Docker Image

  1. Ensure the Tar File Exists: First, we check if we have the tar file that has the Docker image. We usually create this tar file with the docker save command.

  2. Use the docker load Command: Next, we run this command in our terminal:

    docker load -i /path/to/your-image.tar

    We should change /path/to/your-image.tar to the real path of our tar file.

  3. Verify the Loaded Image: After we load the image, we can check if it loaded correctly by running:

    docker images

    This command shows all Docker images we have. We should see our loaded image in the list.

Example

If we saved a Docker image named my-app to a tar file called my-app.tar, we would load it like this:

docker load -i my-app.tar

After loading, we can check our images:

docker images

This shows my-app with its tags. This means the image is now ready to use on our host.

For more information on Docker images and how to manage them, we can look at What are Docker Images and How Do They Work?.

How to Use Docker Save and Docker Load Commands

We can copy Docker images from one host to another without using a repository. The docker save and docker load commands help us with this. These commands let us save a Docker image as a tar file and then load it on another host.

Saving a Docker Image

To save a Docker image to a tar file, we use this command:

docker save -o <path_to_tar_file> <image_name>:<tag>

Example:

docker save -o my_image.tar my_image:latest

This command makes a tar file called my_image.tar. It contains the image my_image with the tag latest.

Loading a Docker Image

To load a Docker image from a tar file, we use this command:

docker load -i <path_to_tar_file>

Example:

docker load -i my_image.tar

This command brings the image from the my_image.tar file into the Docker environment.

Transferring the Tar File

After saving the image to a tar file, we can transfer it to another host. We can use tools like scp, rsync, or any file transfer method that works for us.

For example, we can use scp like this:

scp my_image.tar user@remote_host:/path/to/destination/

Once we transfer the tar file, we need to SSH into the remote host. After that, we can use the docker load command to import the image.

Verifying the Loaded Image

After we load the image, we can check if it is there by listing the available Docker images:

docker images

This will show us the list of images. We will see the one we just loaded. This confirms that the transfer was successful.

How to Verify the Docker Image Transfer

To check if we moved the Docker image between hosts, we can follow these steps:

  1. Check the Docker Images on the Destination Host:
    After we load the image on the new host, we need to list the images. This helps us make sure that the transfer worked.

    docker images

    We should look for the image name and tag in the list.

  2. Inspect the Docker Image:
    We can use the docker inspect command to see details about the image. This includes its ID, size, and how it is set up.

    docker inspect <image_name>:<tag>

    We must change <image_name> and <tag> with the right values.

  3. Run a Container from the Transferred Image:
    Next, we can start a container using the transferred image. This checks if it runs well.

    docker run --rm -it <image_name>:<tag>

    This command runs the container in interactive mode and removes it after we exit. If it runs without any problems, we can say the image transfer worked.

  4. Compare Image Digests:
    If we can access both hosts, we can check the image digests. This helps us make sure they are the same. First, we get the digest of the image on both hosts.

    docker images --digests

    We should compare the digests for the same image and tag on both hosts.

  5. Use Docker History:
    To check if the image layers are the same, we can use the docker history command.

    docker history <image_name>:<tag>

    This shows the history of image layers and commands used to build the image. We can compare the results on both hosts.

By doing these steps, we can verify that the Docker image has moved successfully from one host to another without using a repository. For more on Docker images, we can look at What Are Docker Images and How Do They Work.

Frequently Asked Questions

1. How do we copy a Docker image without a repository?

To copy a Docker image without a repository, we can use the docker save command. This command saves the image as a tar file. Then, we can transfer this tar file to the target host using SCP or another method. After that, we use the docker load command on the destination host to import the image. This way is good for moving images directly between hosts.

2. What is the difference between docker save and docker export?

We use docker save to save a Docker image. It saves all layers of the image as a tar file. We can load this tar file later with docker load. On the other hand, we use docker export to export a container’s filesystem as a tar file. But this does not include image layers or metadata. So, we use docker save for moving images and docker export for container data.

3. Can we transfer Docker images using FTP?

Yes, we can transfer Docker images using FTP. First, we save the Docker image as a tar file with the docker save command. Next, we use an FTP client to upload the tar file to the target host. Finally, we load the image on the destination with the docker load command. This method helps us transfer files between systems easily.

4. How do we verify that a Docker image has been successfully transferred?

To check if a Docker image has transferred well, we can use the docker images command on the destination host after loading the image. This command shows all images. We can see if the transferred image is there. We can also run the image to make sure it works as we expect. This confirms that the transfer was complete and successful.

5. What are the benefits of copying Docker images without a repository?

There are many benefits to copying Docker images without a repository. First, it gives us more security since sensitive images do not go to public or private registries. Second, it allows faster transfers in places without internet. Also, it removes the need for outside services. This makes it good for isolated or secure environments. For more info on Docker, check out what are Docker images and how do they work.