Docker Volumes

Docker volumes are persistent data stores for containers, providing a way to store and manage data independently of a container's lifecycle. Unlike writing data directly to a container's writable layer, volumes do not increase the container's size, making them a preferred choice for data persistence. Volumes can be mounted into multiple containers simultaneously, enabling data sharing.

Key Behaviors

• Named vs. Anonymous Volumes: Volumes can be named (user-defined) or anonymous (Docker assigns a random unique name). Named volumes are explicitly created and reusable, while anonymous volumes are not automatically shared or reused between containers.
• Persistence: When a container is destroyed, its writable layer is lost, but data in both named and anonymous volumes persists unless the container is created with the --rm flag, which removes anonymous volumes upon container removal.
• Non-Empty Volume Mounts: If you mount a non-empty volume into a container's directory, existing files or directories in that container path are not deleted but become inaccessible, hidden by the volume's contents.
• Empty Volume Mounts: If you mount an empty volume into a container directory containing files or directories, those files are copied into the volume by default. If the specified volume does not exist, Docker creates an empty volume automatically.

Docker Volume Commands

Here are common commands for managing Docker volumes:

Create a Volume

docker volume create myvol

Remove a Volume

docker volume rm myvol

List Volumes

docker volume ls

Inspect a Volume

docker volume inspect myvol

Mount a Volume

docker run -it --mount type=volume,src=myvol,dst=/mount/path ubuntu

Or,

docker run -it -v myvol:/mount/path ubuntu

For an anonymous volume, omit the src field (with --mount) or the volume name (with -v):

docker run -it --mount type=volume,dst=/mount/path ubuntu

Or,

docker run -it -v /mount/path ubuntu

To create a container with an anonymous volume that is removed when the container is deleted:

docker run -it --rm --mount type=volume,dst=/mount/path ubuntu