= Docker Volumes =

'''Volumes''' are file objects that `dockerd(8)` manages for a container. While they are written to the host file system, users should only interface with them as a volume name.

Compare to [[Docker/BindMounts|Bind Mounts]].

<<TableOfContents>>

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== Creating Volumes ==

To create a new volume, try:

{{{
docker volume create my-vol
}}}

A container can be created with an existing volume mounted into it.

{{{
docker run --interactive --tty --rm --name my-alpine \
  --mount src=my-vol,dst=/app \
  alpine:latest
}}}

A container can also be created with a new volume.

{{{
docker run --detach --name=my-nginx \
  --mount src=nginx-vol,dst=/usr/share/nginx/html \
  nginx:latest
}}}

The volume is implicitly created ''and'' the contents of the destination directory are written into the newly-initialized volume.

----



== Destroying Volumes ==

After a container is stopped and destroyed, any volumes used will persist. This may or may not be desirable.

To list all volumes, try:

{{{
docker volume ls
}}}

To delete a volume, try:

{{{
docker volume rm my-vol
}}}

----



== Docker Compose ==

Volumes are very common with [[Docker/Compose|Docker Compose]] as the use of a volume abstracts away the local filesystem in a way that sidesteps common issues for reproducibility and reuse.

 * There is no expectation of local directory structure.
 * Filesystem-specific concerns (especially with Zfs or Btrfs) are handled by system [[Docker/Configuration|configurations]].
 * File ownership and permissions are much less likely to become a problem.

To use a volume, create a `docker-compose.yml` file like:

{{{
services:
  app:
    image: node:lts
      - type: volume
        source: myapp
        target: /home/node/app

volumes:
  myapp:
}}}

There is also a shorter syntax.

{{{
services:
  app:
    image: node:lts
    volumes:
      - myapp:/home/node/app

volumes:
  myapp:
}}}

This can create a need to review and manually delete volumes on a recurring basis. See above for details.

----



== Alternative Drivers ==

All of the above examples make use of the '''local volume driver''', which simply means that volumes are managed locally.

Alternative volume drivers exist primarily for distributed and highly available deployments. In some cases, volumes can be shared by multiple containers.

As an example, try:

{{{
docker plugin install --grant-all-permissions vieux/sshfs
docker volume create \
  --driver vieux/sshfs \
  --opt sshcmd=test@node2:/home/test \
  --opt password=testpassword \
  ssh-vol
docker run --detach --name sshfs-container \
  --volume-driver vieux/sshfs \
  --mount src=ssh-vol,dst=/app,volume-opt=sshcmd=test@node2:/home/test,volume-opt=password=testpassword \
  nginx:latest
}}}



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