How to import and export Docker images

This article introduces the import and export of Docker images, which are used in scenarios such as migration, backup, and upgrade. The environment is prepared as follows:

• CentOS 7.0
• Docker 1.18

Introduction to import and export commands

The commands involved are export, import, save, load

save

Order

docker save [options] images [images...]

Example

docker save -o nginx.tar nginx:latest
or
docker save > nginx.tar nginx:latest

The -o and > characters indicate output to a file, nginx.tar is the target file, nginx:latest is the source image name (name:tag).

load

Order
docker load [options]

Example

docker load -i nginx.tar
or
docker load < nginx.tar

-i and < indicate input from a file. The image and related metadata, including tag information, will be successfully imported

export

Order
docker export [options] container

Example
docker export -o nginx-test.tar nginx-test
Where -o means output to a file, nginx-test.tar is the target file, nginx-test is the source container name (name)

import

Order
docker import [options] file|URL|- [REPOSITORY[:TAG]]

Example
docker import nginx-test.tar nginx:imp
or
cat nginx-test.tar | docker import - nginx:imp

The difference is that the tar file exported by the export command is slightly smaller than that exported by the save command.

The export command exports a tar file from a container, while the save command exports from images.

Based on the second point, when the exported file is imported back, the entire history of the image (that is, the information of each layer, if you are not familiar with it, you can read Dockerfile) cannot be retained, and rollback operations cannot be performed; save is based on the image, so the information of each layer can be completely retained when importing. As shown in the following figure, nginx:latest is exported by save and imported by load, nginx:imp is exported by export and imported by import.

suggestion

You can choose commands based on specific usage scenarios

If you just want to back up images, use save and load.

If the container content changes after starting the container and needs to be backed up, use export and import

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