Introduction to import and export operations of docker images

This article will share with you the import and export operations of Docker images, which can be used for migration, backup, upgrade and other scenarios.

The environment is as follows:

CentOS 7.0

Docker 1.18

(Related recommendations: docker tutorial)

Introduction to import and export commands

The commands involved are export, import, save, and load

save

Command

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

Example

docker save -o nginx.tar nginx:latest

or

docker save > nginx.tar nginx:latest

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

load

Command

docker load [options]

export

Command

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

Command

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

Example

docker import nginx-test.tar nginx:imp

or

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

Difference

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

export The command is to export the tar file from the container, while the save command is to export from the image (images)

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

Recommendation

You can choose the command according to the specific usage scenario

If you only want to back up images, just use save and load. After starting the container, if the container content changes and needs to be backed up, use export or import.

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