Docker data persistence management

Options for data persistence

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 <name> from <image> and mount host <hpath> to container <cpath>, read-only
docker container run --mount type=bind,source=<hpath>,target=<cpath>,ro=true --name <name> <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 <name> -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 <name> 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 <name> -i -t <image> /bin/sh

✔️ Use volumes with docker services

# use service name <name>
# start 5 replicas (containers) from the image <image>, mount <volume> to all containers <cpath>
docker service create --name <name> --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)

Data backup with Docker

✔️ Create a container with a volume mount

# create container <name1> from <image>
# mount volume <volume1> to container <cpath1>
# override CMD/ENTRYPOINT directive with <command>
docker container run --name <name1> --mount type=volume,source=<volume1>,target=<cpath1> <image> <command>

✔️ Populate <volume1> with data by accessing container <name1>

✔️ 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> content into <cpath2>/<archive>
docker container run --rm --volumes-from <name1> --mount type=bind,source=<hpath>,target=<cpath2> busybox tar -cvf <cpath2>/<archive> <cpath1>

✔️ As a result, contents of <volume1> will be saved in <hpath>/<archive> on the host

Data restoration with Docker (reverse operation)

✔️ Create a container with a new volume mount

# create container <name2> from <image>
# mount volume <volume2> to container <cpath1>
# override CMD/ENTRYPOINT directive with <command>
docker container run --name <name2> --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> in <cpath1>
docker container run --rm --volumes-from <name2> --mount type=bind,source=<hpath>,target=<cpath2> busybox sh -c "cd <cpath1> && tar -xvf <cpath2>/<archive>"

✔️ As a result, the contents of <archive> has been restored to <volume2>