In the last post we saw that any filesystem change inside a docker container is lost if not commited to the image.

What if we want to share data between containers?

We can use Docker’s Data Volumes and Data Volume Containers.

Data Volumes or Data Volume Containers?

Data Volumes feature allows us to mount a local directory from the host inside a container. That looks good but somehow it breaks the concept of isolation between host and container.

Data Volume Containers create a new container that will store data between container, maintaining the isoltaion between host and containers.

For the sake of simplicity I’ll use Data Volumes in the next examples even if I agree Data Volume Containers are a better way to manage containers data (READ THIS).

Use Data Volumes

To use Data Volumes just add a few options when starting the container:

mkdir dockervolume
echo "test123" > ./dockervolume/test.txt

docker run -i -t -v /root/dockervolume:/volume ubuntuplus /bin/bash

Verify the directory is accessible from inside the container:

root@f4dddb24eb83:/# ls /volume/
test.txt
root@f4dddb24eb83:/# cat /volume/test.txt 
test123
root@f4dddb24eb83:/#

Apply some changes to the file:

root@f4dddb24eb83:/# echo "test456" >> /volume/test.txt                                                      
root@f4dddb24eb83:/# cat /volume/test.txt                                                                    
test123
test456

Now leave the container with CTRL+P CTRL+Q and verify the changes were applied to the host filesystem:

root@ubuntusrv:~# cat ./dockervolume/test.txt 
test123
test456

Great! When can now move on to the next post about Docker networking. Stay tuned!