Volumes

Overview

Volumes are used for decoupling containers from storage and sharing data between containers. When volumes are properly used, data is not lost upon container removal.

Using the VOLUME Instruction in Dockerfile

The VOLUME instruction does not do much by itself, and it is questionable how useful it is. See this, this and this answers for further information.

Sharing Data Between Containers With Docker Volumes

Start by creating a volume:

docker volume create data-volume

Spin up a busybox container that will be removed upon completion, attaching the data directory to the volume you just created. Create a file in the data folder and stop the container:

docker run -it --rm -v data-volume:/data busybox
cd data
touch hello.txt
echo Hello > hello.txt
exit

Spin up a new container by docker run -it --rm -v data-volume:/data busybox and you will be able to verify that your data is not lost. You can even spin up an ubuntu image and the data directory will still be accessible.

Attaching a Directory From Host to a Container

Mounting a local directory is very much same with attaching a volume to a container. Here is an example:

docker run -it --rm -v /Users/kt/delete-me:/data busybox

The host path must be an absolute path. You can use $(pwd) or ("$PWD") to start from the working path, as in $(pwd)/resources.

# Create a volume
docker volume create <volume-name>

# Inspect a volume
docker volume inspect <volume-name>

# List volumes
docker volume ls

# Remove a volume
docker volume rm <volume-name>

# Prune volumes
docker volume prune

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