Understand the differences between Docker containers and images

The difference between Docker containers and images and how to migrate containers and images have always been topics of concern to Docker users. In this article, we will discuss this topic in detail to help readers better understand the differences between Docker containers and images, and master the migration methods of containers and images.

First, let us understand the definitions of Docker containers and images. A Docker image is a static software package that contains code, libraries, and other files needed for runtime. It can be viewed as an executable file that can be used multiple times to create Docker containers. A Docker container is a lightweight, portable software container that contains applications and other dependencies and can be run, stopped, and deleted.

From the above definition, Docker containers and images are two different entities. Although they are related, they are not equivalent. Images are the basis for creating containers, and containers are executable instances.

So, how to migrate containers and images? In Docker, container and image migration can be performed separately.

The first is the migration of the Docker image, which we can use Docker's export and import commands to complete. The following are the steps:

1. First export the image on the source host

docker save -o /tmp/my-image.tar my-image

2. Upload the exported image file to the target host

3. Import the image file on the target host :

docker load -i /tmp/my-image.tar

After completing the above operations, the image will be successfully migrated to the target host.

Next, let’s look at the migration of Docker containers. Migrating Docker containers requires migrating the file system and metadata together. The following are the migration steps:

1. First, stop the container from running on the source host:

docker pause my-container

2. Save the container’s file system.

docker export -o /tmp/my-container.tar my-container

3. Upload the exported container file to the target host.

4. Import the container file system on the target host:

docker import /tmp/my-container.tar my-container

After completing the above operations, the container will be successfully migrated to the target host.

It should be noted that the migration of Docker containers only includes the file system and metadata information of the container, and does not include the persistent storage of data in the container. If you want to migrate the container's data, you need to save them to the host before proceeding.

The difference between Docker containers and images and how to migrate containers and images are important things that Docker users need to understand. I hope this article can solve relevant problems for readers and help them better use Docker technology.

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