Backup all mounted volumes in a Docker container into a .tar.gz archive

backup-container-volumes.sh

#!/bin/bash

# Author: @DrJume

# This script lets you backup all mounted volumes of a Docker container
# into a .tar.xz archive.


# Throw on nonzero exit in pipelines
set -e

# Throw on paramter expansion on unset variables.
set -u

# log every exectued command
# set -x # during dev


printUsage() {
  cat <<EOF >/dev/stderr

Usage:  $0 container_id|container_name [backup_destination] [-xz compression_level]

  container_id,           ID or name of a Docker container.
  container_name

  backup_destination      Path to where to create the tarball.
                          Default: . (current working dir)
EOF
}

if [[ $# -lt 1 ]]; then
  printUsage
  exit 1
fi

CONTAINER="$1"

BACKUP_DESTINATION=$PWD
if [[ -n ${2:-} ]]; then
  BACKUP_DESTINATION+="/${2:-}"
fi

# check if Docker container exists
if ! docker inspect $CONTAINER > /dev/null ; then
  echo "No such container: $CONTAINER"
  exit 2
fi

MOUNTS=($(docker inspect --format="{{range .Mounts}}{{.Destination}} {{end}}" $CONTAINER))
VOLUMES_NAMES=($(docker inspect --format="{{range .Mounts}}{{.Name}} {{end}}" $CONTAINER))

TRANSFORM_EXPR=()
for i in "${!MOUNTS[@]}"; do
  mount=${MOUNTS[$i]#/} # strip leading '/'
  volume_name=${VOLUMES_NAMES[$i]}
  TRANSFORM_EXPR+=("--transform='s,^$mount,${volume_name:-mount},'")
done
unset mount
unset volume_name

TAR_CMD="tar -czvf /backup/${CONTAINER}_$(date +%F_%H-%M-%S).tar.gz ${TRANSFORM_EXPR[*]} --show-transformed-names ${MOUNTS[*]}"

echo "Running: $TAR_CMD"
read -s -n 1 -p "Press any key to continue..."; echo

# attach all volumes from container as read-only (:ro)
( docker run --rm --volumes-from "$CONTAINER:ro" -v "$BACKUP_DESTINATION:/backup" --name "${CONTAINER}_backup" ubuntu bash -c "$TAR_CMD" ) \
    | less -P "Press 'q' to continue..."