Docker : Use Persistent Storage2018/05/30

	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]	This example is based on the environment that SELnux is Permissive or Disabled.
[2]	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              c0e7b10a1ad9        9 seconds ago       1.15 MB
web_server               latest              e0fe7c3805c4        7 minutes ago       482 MB
srv.world/fedora_httpd   latest              f153182d83f9        14 minutes ago      525 MB
docker.io/busybox        latest              8c811b4aec35        6 days ago          1.15 MB
docker.io/fedora         latest              cc510acfcd70        3 weeks ago         253 MB

# generate a Container with any name you like

[root@dlp ~]#

docker run -it --name storage_server storage

/ #

exit

[3]	To use the Container above as a Storage Server from other Containers, add an option [--volumes-from].

[root@dlp ~]#

docker run -it --name fedora_server --volumes-from storage_server fedora /bin/bash

[root@18ffc7259932 /]#

df -hT

Filesystem              Type     Size  Used Avail Use% Mounted on
overlay                 overlay   15G  2.9G   13G  19% /
tmpfs                   tmpfs    4.9G     0  4.9G   0% /dev
tmpfs                   tmpfs    4.9G     0  4.9G   0% /sys/fs/cgroup
/dev/mapper/fedora-root xfs       15G  2.9G   13G  19% /storage
shm                     tmpfs     64M     0   64M   0% /dev/shm
tmpfs                   tmpfs    4.9G     0  4.9G   0% /proc/scsi
tmpfs                   tmpfs    4.9G     0  4.9G   0% /sys/firmware

[root@18ffc7259932 /]#

echo "persistent storage" >> /storage/testfile.txt

[root@18ffc7259932 /]#

ls -l /storage

total 4
-rw-r--r--. 1 root root 19 May 30 08:07 testfile.txt

[4]	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

[5]	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 fedora /bin/bash

[root@86d81745d2d3 /]#

df -hT

Filesystem              Type     Size  Used Avail Use% Mounted on
overlay                 overlay   15G  2.9G   13G  19% /
tmpfs                   tmpfs    4.9G     0  4.9G   0% /dev
tmpfs                   tmpfs    4.9G     0  4.9G   0% /sys/fs/cgroup
/dev/mapper/fedora-root xfs       15G  2.9G   13G  19% /mnt
shm                     tmpfs     64M     0   64M   0% /dev/shm
tmpfs                   tmpfs    4.9G     0  4.9G   0% /proc/scsi
tmpfs                   tmpfs    4.9G     0  4.9G   0% /sys/firmware

[root@86d81745d2d3 /]#

cat /mnt/testfile.txt

persistent storage

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