README.md

docker-volumes.sh

The docker export and docker commit commands do not save the container volumes. Use this script to save and load the container volumes.

Usage

docker-volumes.sh [-v|--verbose] CONTAINER [save|load] TARBALL

Podman

To use Podman instead of Docker, prepend DOCKER=podman to the command line to set the DOCKER environment variable.

Example

Let's migrate a container to another host with all its volumes.

# Stop the container 
docker stop $CONTAINER
# Create a new image
docker commit $CONTAINER $CONTAINER
# Save and load image to another host
docker save $CONTAINER | ssh $USER@$HOST docker load 

# Save the volumes (use ".tar.gz" if you want compression)
docker-volumes.sh $CONTAINER save $CONTAINER-volumes.tar

# Copy volumes to another host
scp $CONTAINER-volumes.tar $USER@$HOST:

### On the other host:

# Create container with the same options used in the previous container
docker create --name $CONTAINER [<PREVIOUS CONTAINER OPTIONS>] $CONTAINER

# Load the volumes
docker-volumes.sh $CONTAINER load $CONTAINER-volumes.tar

# Start container
docker start $CONTAINER

Notes

• This script could have been written in Python or Go, but the tarfile module and the tar package lack support for writing sparse files.
• We use the Ubuntu 22.04 Docker image with GNU tar v1.29 that uses SEEK_DATA/SEEK_HOLE to manage sparse files.
• To see the volumes that would be processed run docker container inspect -f '{{json .Mounts}}' $CONTAINER and pipe it to either jq or python -m json.tool.

Bugs / Features

• Make sure the volumes are defined as such with the VOLUME directive. For example, the Apache image lacks them, but you can add them manually with docker commit --change 'VOLUME /usr/local/apache2/htdocs' $CONTAINER $CONTAINER