labs-07.md

Labs: Volumes

List the Volumes

Are there any volumes defined by default?

docker volume ls

Create a Host Volume

First, create a directory and run a container with that directory mapped as a host volume:

mkdir ${HOME}/data
cd ${HOME}/data
echo hello host >host.txt
docker container run -it --rm -u 1000:1000 -v "$(pwd):/data" busybox /bin/sh

Inside that container, try to view the contents of the directory. What happens if you try to write to a file in the volume?

ls -al /data
cat /data/host.txt
echo hello container >/data/container.txt
exit

Try running the container as root and writing to the file again:

docker container run -it --rm -v "$(pwd):/data" busybox /bin/sh
echo hello container >/data/container.txt
ls -al /data
exit

Create a Named Volume

Try creating some volumes in different ways:

docker volume create by-hand
docker container run --rm -v dynamic:/data busybox ls -l /data
docker volume ls

What files were included in "dynamic" volume? Lets try manually loading some content into the volume with a "utility container":

cd $HOME/training-labs/volume-example
ls -al data
tar -cC data . | docker run -i --rm -v dynamic:/target busybox tar -xC /target

And then lets run the same container as before, but now with the volume populated:

docker container run -it --rm -v dynamic:/data busybox /bin/sh
ls -al /data
echo hello container >/data/container.txt
exit
docker container run --rm -v dynamic:/data busybox ls -al /data

Did the data persist across multiple containers?

Initialize a Named Volume From an Image

Take a look at the Dockerfile in the volume-example directory, then build the image:

docker image build -t volume-ex:latest .

Without defining a volume, verify the contents of the image:

docker container run --rm volume-ex:latest ls -al /image-data

Now run a container with a volume defined:

docker container run -it --rm -v image-data:/image-data volume-ex
ls -l /image-data
echo hello container >/image-data/container.txt
exit

Did you have any errors creating files inside the container with the named volume, even with the change of UID? Where did the initial contents of the volume come from?

Run another container to verify your changes are still there:

docker container run --rm -v image-data:/image-data volume-ex ls -l /image-data

What happens if you mounted a different volume in that location?

docker container run --rm -v dynamic:/image-data volume-ex ls -l /image-data

Are the contents of the image visible when you mount the other volume?

Create an Anonymous Volume

Where does docker store the volume defined below?

docker container run --rm -v /image-data volume-ex ls -l /image-data

Have a look at your volume list now:

docker volume ls

If you have multiple anonymous volumes, how can you identify which belong to each container, and which are safe to delete?