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[SOLVED] How to copy Docker images from one host to another without using a repository - docker

[SOLVED] Easy Ways to Transfer Docker Images Between Hosts Without a Repository

In this chapter, we will look at simple ways to copy Docker images from one host to another without using a repository. Knowing how to do this is important for developers and system admins. They need to manage Docker images easily across different environments without using outside registries. This guide will show us six easy methods for moving Docker images directly between hosts. This way, we can keep our work flowing smoothly.

Here are the methods we will talk about:

  • Solution 1: Save Docker image to a tar file
  • Solution 2: Transfer the tar file using SCP
  • Solution 3: Load the Docker image from the tar file
  • Solution 4: Use Docker save and load in one command
  • Solution 5: Copy Docker images using a USB drive
  • Solution 6: Use a Docker registry as a temporary solution

Each method gives a different way to transfer Docker images. This helps us choose the best one for our needs. For more tips about Docker, we can check our articles on how to copy files from host to Docker or communication between Docker containers. Let’s get into the details of each method!

Solution 1 - Save Docker image to a tar file

To copy Docker images from one host to another without using a repository, we first need to save the Docker image to a tar file. This helps us create a version of the image that we can move easily.

Steps to Save a Docker Image to a Tar File

  1. Identify the Docker Image: First, we need to find the name or ID of the Docker image we want to save. We can list all Docker images with this command:

    docker images

    This command shows a list of images with their names, tags, and IDs.

  2. Use the docker save Command: After we find the image, we can save it to a tar file using the docker save command. We replace <image_name> with the name of our image and <output_file>.tar with the name we want for our tar file.

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

    For example, to save an image called my_app:latest, we run:

    docker save -o my_app.tar my_app:latest

Important Notes

  • The tar file we create will have all layers and metadata of the Docker image. This makes sure we can fully restore the image later.
  • This method is very useful for moving Docker images between different environments. For example, we can move from a local development machine to a production server.

After we save the image as a tar file, we can transfer it to another host using different methods. We will discuss these methods in the next solutions.

For more details on working with Docker images, we can check what are Docker images.

Solution 2 - Transfer the tar file using SCP

We can transfer the Docker image tar file from one host to another without using a repository. We will use Secure Copy Protocol (SCP). This method is safe and works well for moving files over SSH.

Steps to Transfer the Docker Image Tar File Using SCP

  1. Check if SCP is Installed: Most Linux systems have SCP already installed. We can check if SCP is there by running:

    scp -V

  2. Transfer the Tar File: We will use the scp command to move the tar file from the source host to the destination host. The general format is:

    scp /path/to/your/image.tar username@destination_host:/path/to/destination/

    We need to replace the placeholders with the real values:

    • /path/to/your/image.tar: This is the path of your tar file on the source host.
    • username: This is your username on the destination host.
    • destination_host: This is the IP address or name of the destination host.
    • /path/to/destination/: This is where we want to save the tar file on the destination host.

    For example, we can write:

    scp my_image.tar user@192.168.1.2:/home/user/

  3. Log In: We might need to type the password for the user on the destination host. After we log in, the transfer will start.

  4. Check Transfer: When the transfer is done, we can check if the tar file is on the destination host. We can do this by connecting to it and listing the directory:

    ssh username@destination_host
ls /path/to/destination/

Notes

  • We should make sure that SSH is on for the destination host. Also, the firewall should allow connections on port 22. This is the default for SSH.

  • If we are moving large files, we can add the -C option with SCP to turn on compression. This can make the transfer faster:

    scp -C /path/to/your/image.tar username@destination_host:/path/to/destination/

This way is simple and works well for moving Docker images as tar files from one host to another safely. For more help on handling Docker images, we can check our guide on how to copy files from host to Docker.

Solution 3 - Load the Docker image from the tar file

We have to load the Docker image from the tar file after we move it to the target host. We can use methods like SCP or a USB drive. This step lets us use the Docker image without pulling it from a repository.

Steps to Load the Docker Image

  1. Open a Terminal: First, we need to open the terminal on our target Docker host.

  2. Navigate to the Directory: Next, we go to the place where we put the tar file. For example, if we put it in the /tmp folder, we can use this command:

    cd /tmp

  3. Load the Docker Image: Now we can use the docker load command to import the image from the tar file. The command looks like this:

    docker load -i <image-file-name>.tar

    We replace <image-file-name> with the name of our tar file. For example:

    docker load -i my_image.tar

  4. Verify the Loaded Image: After we load the image, we should check if it is imported. We can list all images using:

    docker images

    This command shows all Docker images. We should see our loaded image in this list.

Example

Here is a full example if our tar file is named webapp_image.tar:

cd /tmp
docker load -i webapp_image.tar
docker images

Notes

  • We need to make sure the Docker daemon is running on the target host before we run the docker load command.

  • If there are any permission problems, we might need to add sudo before our Docker commands, like this:

    sudo docker load -i webapp_image.tar

By following these steps, we can load a Docker image from a tar file on our target host. This lets us run our applications without depending on an external Docker repository. For more details about managing Docker images, we can check the article on what are Docker images.

Solution 4 - Use Docker Save and Load in One Command

We can copy Docker images from one host to another using just one command. We do this by combining docker save and docker load. This way, we save the Docker image to a tar file. Then, we load it directly on the destination host without saving it on the filesystem.

Steps to Use Docker Save and Load in One Command

  1. Use SSH to Execute the Command Remotely: We can pipe commands over SSH. This lets us save the image on the source host and load it on the target host at the same time. Here’s how we can do this:

    docker save <image_name> | ssh user@destination_host "docker load"

    We need to replace <image_name> with the name of our Docker image. Also, replace user@destination_host with the correct SSH user and hostname or IP address of the destination host.

  2. Example: Let’s say we have an image named myapp:latest. The command will look like this:

    docker save myapp:latest | ssh user@192.168.1.50 "docker load"

    This command saves the myapp:latest image. It sends it directly to the destination host at IP 192.168.1.50. There, it will be loaded into Docker.

Notes:

  • We must have SSH access to the destination host. Also, Docker should be installed on both hosts.

  • If we want to use a different Docker daemon or setup on the destination host, we can add the -H flag in the docker load command:

    docker save <image_name> | ssh user@destination_host "docker -H tcp://anotherhost:2375 load"

  • This method is good because it skips the need for temporary files on disk. It also saves time when we transfer images between hosts.

By using the docker save and docker load commands like this, we can copy Docker images between hosts easily. We do not need an extra repository. If we want more information about managing Docker images, we can check the article on what are Docker images.

Solution 5 - Copy Docker images using a USB drive

Copying Docker images with a USB drive is a simple way to move images between hosts. This is useful when the network is not working or is very slow. We can save the Docker image to a tar file, move it to the USB drive, and then load it on the other host.

Step 1: Save Docker Image to a Tar File

First, we save the Docker image from the source host to a tar file. We do this with the docker save command. We need to replace <image_name> with the name of our Docker image and <output_file> with the name we want for our tar file.

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

For example, if we have an image called myapp:latest and we want to save it as myapp.tar, we run:

docker save -o myapp.tar myapp:latest

Step 2: Transfer the Tar File to a USB Drive

  1. Insert the USB Drive: Plug the USB drive into the source host.
  2. Mount the USB Drive: Make sure the USB drive is mounted. We can usually find it under /media/username/ or /mnt/.
  3. Copy the Tar File: We use the cp command to copy the tar file to the USB drive.
cp <output_file>.tar /media/username/<usb_drive>/

For example:

cp myapp.tar /media/username/usb_drive/

Step 3: Load the Docker Image from the Tar File on the Destination Host

After we safely eject the USB drive from the source host, we plug it into the destination host. We need to mount the USB drive on the destination host if it is not mounted automatically.

  1. Mount the USB Drive: Make sure the USB drive is ready to use.
  2. Copy the Tar File to the Destination Host: Move the tar file from the USB drive to a folder on the destination host.
cp /media/username/<usb_drive>/<output_file>.tar /path/to/destination/

For example:

cp /media/username/usb_drive/myapp.tar /home/user/
  1. Load the Docker Image: We use the docker load command to load the image from the tar file.
docker load -i /path/to/destination/<output_file>.tar

Following the example:

docker load -i /home/user/myapp.tar

Conclusion

Using a USB drive to copy Docker images is a good way when we cannot use a network. This method helps us move images easily and makes sure the destination host has the right Docker images without needing a repository. If we want to manage our Docker images better, we can look into Docker registries or other ways to transfer images.

Solution 6 - Use a Docker registry as a temporary solution

If we need to copy Docker images from one host to another and do not have a permanent repository, we can use a Docker registry. This is a good temporary solution. It allows us to push our Docker images to a local or private registry. Then we can pull them from the destination host.

Step 1: Set Up a Local Docker Registry

First, we must set up a Docker registry. We can run a local Docker registry with the official Docker registry image. We should run this command on the host where we want to set up the registry:

docker run -d -p 5000:5000 --restart=always --name registry registry:2

This command makes a Docker registry container that we can reach at http://localhost:5000. If we want to access it over a network, we may need to change our firewall or network settings.

Step 2: Tag Your Docker Image

Next, we need to tag the Docker image we want to copy. This makes it point to the local registry. Let’s say our image is named my-image:latest. We can tag it like this:

docker tag my-image:latest localhost:5000/my-image:latest

Step 3: Push the Image to the Registry

Now that we tagged the image for our local registry, we can push it using this command:

docker push localhost:5000/my-image:latest

This command uploads the image to our local Docker registry.

Step 4: Pull the Image on the Destination Host

On the destination host, we need to pull the image from our local registry. If the destination host can reach the registry, we use this command:

docker pull localhost:5000/my-image:latest

If we are accessing the registry from a different host, we should change localhost to the IP address or hostname of the registry host.

Step 5: Run the Docker Image

After we pull the image successfully, we can run it on the destination host:

docker run -d --name my-container localhost:5000/my-image:latest

Additional Considerations

  • Make sure Docker is running on both hosts and they can talk to each other.
  • If we use a firewall or security group, we need to allow traffic on the registry port. The default is 5000.
  • Think about securing our registry with HTTPS for production uses.
  • This method is good for temporary cases. For more permanent solutions, we can look into using a dedicated Docker registry service like Docker Hub or other private registries.

By following these steps, we can easily copy Docker images between hosts using a Docker registry as a temporary solution. This method makes it easier without needing a public repository and helps us manage our Docker images better. If we want to learn more about Docker registries, we can check other resources.

Conclusion

In this article, we looked at different ways to copy Docker images from one host to another. We do not use a repository for this.

We can save Docker images to tar files. Then we can transfer them using SCP. Also, we can use USB drives. These are good solutions for developers.

If we want more options, we can think about using a Docker registry for a short time. These methods help us work better and give us more flexibility. They make it easy to transfer Docker images.

For more tips on Docker, we can check our guides on copying files from host to Docker and communicating between Docker containers.

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