Ubuntu 18.04
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Docker : Use Persistent Storage
2018/06/12
 
When Container is removed, data in it are also lost, so it's necessary to use external filesystem in Container as persistent storage if you need.
[1] For exmaple, create a Container only for using to save data as a storage server with an image busybox.
root@dlp:~#
vi Dockerfile
# create new

FROM busybox
MAINTAINER ServerWorld <admin@srv.world>

VOLUME /storage
CMD /bin/sh

# build image

root@dlp:~#
docker build -t storage ./
root@dlp:~#
docker images

REPOSITORY                 TAG           IMAGE ID            CREATED             SIZE
storage                    latest        f250059f0ff5        12 seconds ago      1.15MB
web_server                 latest        46fdaf40a0fe        6 minutes ago       313MB
srv.world/ubuntu_apache2   latest        b2d00f9d9fb4        About an hour ago   218MB
ubuntu                     latest        113a43faa138        6 days ago          81.2MB
busybox                    latest        8c811b4aec35        2 weeks ago         1.15MB

# generate a Container with any name you like

root@dlp:~#
docker run -it --name storage_server storage

/ #
exit
[2] To use the Container above as a Storage Server from other Containers, add an option [--volumes-from].
root@dlp:~#
docker run -it --name ubuntu_server --volumes-from storage_server ubuntu /bin/bash
root@d36cc3eadc2f:/#
df -hT

Filesystem                  Type     Size  Used Avail Use% Mounted on
overlay                     overlay   78G  2.8G   71G   4% /
tmpfs                       tmpfs     64M     0   64M   0% /dev
tmpfs                       tmpfs    8.9G     0  8.9G   0% /sys/fs/cgroup
/dev/mapper/ubuntu--vg-root ext4      78G  2.8G   71G   4% /storage
shm                         tmpfs     64M     0   64M   0% /dev/shm
tmpfs                       tmpfs    8.9G     0  8.9G   0% /proc/scsi
tmpfs                       tmpfs    8.9G     0  8.9G   0% /sys/firmware

root@d36cc3eadc2f:/#
echo "persistent storage" >> /storage/testfile.txt

root@d36cc3eadc2f:/#
ls -l /storage

total 4
-rw-r--r-- 1 root root 19 Jun 12 02:26 testfile.txt
[3] Make sure datas are saved to run a Container of Storage Server like follows.
root@dlp:~#
docker start storage_server

root@dlp:~#
docker exec -it storage_server cat /storage/testfile.txt

persistent storage
[4] For other way to save data in external filesystem, it's possible to mount a directory on Docker Host into Containers.
# create a directory

root@dlp:~#
mkdir -p /var/lib/docker/disk01

root@dlp:~#
echo "persistent storage" >> /var/lib/docker/disk01/testfile.txt
# run a Container with mounting the directory above on /mnt

root@dlp:~#
docker run -it -v /var/lib/docker/disk01:/mnt ubuntu /bin/bash
root@4526babc56ec:/#
df -hT

Filesystem                  Type     Size  Used Avail Use% Mounted on
overlay                     overlay   78G  2.8G   71G   4% /
tmpfs                       tmpfs     64M     0   64M   0% /dev
tmpfs                       tmpfs    8.9G     0  8.9G   0% /sys/fs/cgroup
/dev/mapper/ubuntu--vg-root ext4      78G  2.8G   71G   4% /mnt
shm                         tmpfs     64M     0   64M   0% /dev/shm
tmpfs                       tmpfs    8.9G     0  8.9G   0% /proc/scsi
tmpfs                       tmpfs    8.9G     0  8.9G   0% /sys/firmware

root@4526babc56ec:/#
cat /mnt/testfile.txt

persistent storage
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