How to port data-only volumes from one host to another?

Question

The official answer is available in the section "Backup, restore, or migrate data volumes":

BACKUP:

sudo docker run --rm --volumes-from DATA -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data

• --rm: remove the container when it exits
• --volumes-from DATA: attach to the volumes shared by the DATA container
• -v $(pwd):/backup: bind mount the current directory into the container; to write the tar file to
• busybox: a small simpler image - good for quick maintenance
• tar cvf /backup/backup.tar /data: creates an uncompressed tar file of all the files in the /data directory

RESTORE:

# create a new data container
$ sudo docker create -v /data --name DATA2 busybox true
# untar the backup files into the new container᾿s data volume
$ sudo docker run --rm --volumes-from DATA2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
data/
data/sven.txt
# compare to the original container
$ sudo docker run --rm --volumes-from DATA -v `pwd`:/backup busybox ls /data
sven.txt

Extending the official answer from Docker docs and the top answer here, you can have following functions in your .bashrc or .zshrc:

# backup files from a docker volume into /tmp/backup.tar.gz
function docker-volume-backup-compressed() {
  docker run --rm -v /tmp:/backup --volumes-from "$1" debian:jessie tar -czvf /backup/backup.tar.gz "${@:2}"
}

# restore files from /tmp/backup.tar.gz into a docker volume
function docker-volume-restore-compressed() {
  docker run --rm -v /tmp:/backup --volumes-from "$1" debian:jessie tar -xzvf /backup/backup.tar.gz "${@:2}"
  echo "Double checking files..."
  docker run --rm -v /tmp:/backup --volumes-from "$1" debian:jessie ls -lh "${@:2}"
}

# backup files from a docker volume into /tmp/backup.tar
function docker-volume-backup() {
  docker run --rm -v /tmp:/backup --volumes-from "$1" busybox tar -cvf /backup/backup.tar "${@:2}"
}

# restore files from /tmp/backup.tar into a docker volume
function docker-volume-restore() {
  docker run --rm -v /tmp:/backup --volumes-from "$1" busybox tar -xvf /backup/backup.tar "${@:2}"
  echo "Double checking files..."
  docker run --rm -v /tmp:/backup --volumes-from "$1" busybox ls -lh "${@:2}"
}

Note that the backup is saved into /tmp, so you can move the backup file saved there between docker hosts.

There is also two pairs of backup/restore aliases. One using compression and debian:jessie and other with no compression but with busybox. Favor using compression if the files to backup are big.

You can export the volume to tar and transfer to another machine. And import the data with tar on the second machine. This does not rely on implementation details of the volumes.

# you can list shared directories of the data container
docker inspect <data container> | grep "/vfs/dir/"

# you can export data container directory to tgz
docker run --cidfile=id.tmp --volumes-from <data container> ubuntu tar -cO <volume path> | gzip -c > volume.tgz

# clean up: remove exited container used for export and temporary file
docker rm `cat id.tmp` && rm -f id.tmp

I'll add another recent tool here from IBM which is actually made for the volume migration from one container host to another. This is a currently on-going project. So, you may find a different version with additional features in future.

Cargo was developed to migrate containers from one host to another host along with their data with minimal downtime. Cargo uses data federation capabilities of union filesystem to create a unified view of data (mainly the root file system) across the source and target hosts. This allows Cargo to start up a container almost immediately (within milliseconds) on the target host as the data from source root file system gets copied to target hosts either on-demand (using a copy-on-write (COW) partition) or lazily in the background (using rsync).

Important points are: - a centralized server handles the migration process

The link to the project is given here:

https://github.com/nadgowdas/cargo

In case your machines are in different VPCs or you want to copy from/to local machine (like in my case) you can use dvsync I created. It's basically ngrok combined with rsync over SSH packaged into two small (both ~25MB) images. First, you start the dvsync-server on a machine you want to copy data from (You'll need the NGROK_AUTHTOKEN which can be obtained from ngrok dashboard):

$ docker run --rm -e NGROK_AUTHTOKEN="$NGROK_AUTHTOKEN" \
  --mount source=MY_VOLUME,target=/data,readonly \
  quay.io/suda/dvsync-server

Then you can start the dvsync-client on the machine you want to copy the files to, passing the DVSYNC_TOKEN shown by the server:

docker run -e DVSYNC_TOKEN="$DVSYNC_TOKEN" \
  --mount source=MY_TARGET_VOLUME,target=/data \
  quay.io/suda/dvsync-client 

Once the copying will be done, the client will exit. This works with Docker CLI, Compose, Swarm and Kubernetes as well.

Here's a one-liner in case it can be established an SSH connection between the machines:

docker run --rm -v <SOURCE_DATA_VOLUME_NAME>:/from alpine ash -c "cd /from ; tar -cf - . " | ssh <TARGET_HOST> 'docker run --rm -i -v <TARGET_DATA_VOLUME_NAME>:/to alpine ash -c "cd /to ; tar -xpvf - " '

Credits go to Guido Diepen's post.