Import from rootfs archive
Format: docker import [options] <file>|<URL>|- [<repository name>[:<label>]]
The tarball can be a local file, a remote web file, or even from standard input. The tarball will be expanded in the mirror / directory and submitted directly as the first layer of the mirror.
Let’s say we want to create a mirror of an Ubuntu 16.04 template for OpenVZ:
$ docker import \
http://download.openvz.org/template/precreated/ubuntu-16.04-x86_64.tar.gz \
openvz/ubuntu:16.04
Downloading from http://download.openvz.org/template/precreated/ubuntu-16.04-x86_64.tar.gz
sha256:412b8fc3e3f786dca0197834a698932b9c51b69bd8cf49e100c35d38c9879213 This command automatically downloads the ubuntu-16.04-x86_64.tar.gz file, expands it as the root filesystem, and saves it as the image openvz/ubuntu:16.04.
After the import is successful, we can see the imported image using docker image ls:
$ docker image ls openvz/ubuntu
REPOSITORY TAG IMAGE ID CREATED SIZE
openvz/ubuntu 16.04 412b8fc3e3f7 55 seconds ago 505MB If we look at its history, we’ll see that there are links to the imported files in the description:
$ docker history openvz/ubuntu:16.04
IMAGE CREATED CREATED BY SIZE COMMENT
f477a6e18e98 About a minute ago 214.9 MB Imported from http://download.openvz.org/template/precreated/ubuntu-16.04-x86_64.tar.gz Importing and Exporting Docker Images – docker save and docker load
Docker also provides the docker save and docker load commands for saving an image as a file, transferring it to another location, and then loading it in. This was the practice when there was no Docker Registry, but it is no longer recommended and image migrations should be done directly using the Docker Registry, either directly from the Docker Hub or from a private intranet registry.
Saving Images
Use the docker save command to save an image as an archive.
For example, we want to save this alpine image.
$ docker image ls alpine
REPOSITORY TAG IMAGE ID CREATED SIZE
alpine latest baa5d63471ea 5 weeks ago 4.803 MB $ docker save alpine -o filename
$ file filename
filename: POSIX tar archive The filename here can be any name or even any extension, but the file is an archive by nature.
Note: If the same name is used, it will be overwritten (without warning).
If you use gzip compression:
$ docker save alpine | gzip > alpine-latest.tar.gz Then we copied the alpine-latest.tar.gz file to another machine where we can load the image with the following command:
$ docker load -i alpine-latest.tar.gz
Loaded image: alpine:latest If we combine these two commands with ssh and pv, using Linux’s powerful pipelines, we can write a command to migrate an image from one machine to another with a progress bar:
docker save <image name> | bzip2 | pv | ssh <username>@<hostname> ‘cat | docker load’
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