Concept of Docker Volumes

Remarks#

People new to Docker often don’t realize that Docker filesystems are temporary by default. If you start up a Docker image you’ll get a container that on the surface behaves much like a virtual machine. You can create, modify, and delete files. However, unlike a virtual machine, if you stop the container and start it up again, all your changes will be lost — any files you previously deleted will now be back, and any new files or edits you made won’t be present.

Volumes in docker containers allow for persistent data, and for sharing host-machine data inside a container.

A) Launch a container with a volume

[root@localhost ~]# docker run -it -v  /data  --name=vol3   8251da35e7a7 /bin/bash
root@d87bf9607836:/# cd /data/
root@d87bf9607836:/data# touch abc{1..10}
root@d87bf9607836:/data# ls

abc1 abc10 abc2 abc3 abc4 abc5 abc6 abc7 abc8 abc9

B) Now press [cont +P+Q] to move out from container without terminating the container checking for container that is running

[root@localhost ~]# docker ps

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES d87bf9607836 8251da35e7a7 “/bin/bash” About a minute ago Up 31 seconds vol3 [root@localhost ~]#

C) Run ‘docker inspect’ to check out more info about the volume

[root@localhost ~]# docker inspect  d87bf9607836

“Mounts”: [ { “Name”: “cdf78fbf79a7c9363948e133abe4c572734cd788c95d36edea0448094ec9121c”, “Source”: “/var/lib/docker/volumes/cdf78fbf79a7c9363948e133abe4c572734cd788c95d36edea0448094ec9121c/_data”, “Destination”: “/data”, “Driver”: “local”, “Mode”: "", “RW”: true

D) You can attach a running containers volume to another containers

[root@localhost ~]# docker run -it  --volumes-from  vol3  8251da35e7a7  /bin/bash

root@ef2f5cc545be:/# ls

bin boot data dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var

root@ef2f5cc545be:/# ls /data abc1 abc10 abc2 abc3 abc4 abc5 abc6 abc7 abc8 abc9

E) You can also mount you base directory inside container

[root@localhost ~]# docker run -it  -v  /etc:/etc1 8251da35e7a7 /bin/bash

Here: /etc is host machine directory and /etc1 is the target inside container