Docker data persistence management

Manage data persistence with docker

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Options for data persistence

Table of contents

  1. Bind-mounts
  2. Volumes
  3. Backup data
  4. Restore data

Bind-mounts

  • Always use the --mount syntax instead of -v when using bind mounts.
  • Host paths and container paths must always be absolute paths (use command substitution with realpath for convenience).
  • host mounted directory contents will replace bind mount contents in container (CAUTION).
  • Use bind-mounts with docker containers :
# create container $container from $image and mount host $hpath to container $cpath, read-only
docker container run --mount "type=bind,source=$hpath,target=$cpath,ro=true" --name "$container" "$image"

# same as above plus : override CMD/ENTRYPOINT directive with interactive shell/pseudo tty
docker container run --mount "type=bind,source=$hpath,target=$cpath,ro=true" --name "$container" -i -t "$image" /bin/sh

Volumes

  • Always use the --mount syntax instead of -v when using volumes as well (only option supported by docker service).
  • Easier to back up or migrate, manageable using Docker CLI commands, shared among multiple containers, higher performance on non-Linux.
  • Volumes do not increase the size of the containers using them, and their contents are persisted once the container is removed.
  • volume name must be unique on a given host machine, and they are automatically created on invocation if they do not exist.
  • Manage volumes :
# create volume
docker volume create "$volume"

# remove volume
docker volume rm "$volume"

# inspect volume
docker volume inspect "$volume"
  • Volume contents is stored on the host's file system in the "Mountpoint" location of the docker volume inspect output.
  • Use volumes with docker containers :
# create container $container from $image and mount volume $volume to container $cpath
# override CMD/ENTRYPOINT directive with interactive shell/pseudo tty
docker run --rm --mount "type=volume,source=$volume,target=$cpath" --name "$container" -i -t "$image" /bin/sh
  • Use volumes with docker services :
# use service name $container
# start 5 replicas (containers) from the image $image, mount $volume to all containers $cpath
docker service create --name "$container" --replicas=5 --mount "type=volume,source=$volume,target=$cpath" "$image"

In the above case, each container in the service will access its own local volume (the default volume driver local does not support shared storage).

Backup data

  • Create a container with a volume mount :
# create container $container1 from $image
# mount volume $volume1 to container $cpath1
# override CMD/ENTRYPOINT directive with $command
docker container run --name "$container1" --mount "type=volume,source=$volume1,target=$cpath1" "$image" "$command"
  • Populate $volume1 with data by accessing container $container1.
  • Create a dedicated backup container :
# create unnamed disposable container from busybox
# mount volume $volume1 to container $cpath1
# mount host $hpath to container $cpath2
# run a tar command to create an archive of $cpath1 contents into $cpath2/$archive.tar
docker container run --rm --volumes-from "$container1" --mount "type=bind,source=$hpath,target=$cpath2" busybox tar -cvf "$cpath2/$archive.tar" "$cpath1"
  • As a result, contents of $volume1 will be saved in $hpath/$archive.tar on the host.

Restore data

  • Create a container with a new volume mount :
# create container $container2 from $image
# mount volume $volume2 to container $cpath1
# override CMD/ENTRYPOINT directive with $command
docker container run --name "$container2" --mount "type=volume,source=$volume2,target=$cpath1" "$image" "$command"
  • Create a dedicated restoration container :
# create unnamed disposable container from busybox
# mount volume $volume2 to container $cpath1
# mount host $hpath to container $cpath2
# run a tar command to extract $cpath2/$archive.tar in $cpath1
docker container run --rm --volumes-from "$container2" --mount "type=bind,source=$hpath,target=$cpath2" busybox sh -c "cd $cpath1 && tar -xvf $cpath2/$archive.tar"
  • As a result, the contents of $archive has been restored to <volume2>.