What is the difference between a volume and a simple bind mount to a directory on the host?

• Volumes: The lifecycle of a volume is separate from the lifecycle of a container. Docker manages the storage of volumes on the host machine. Volumes are created, mounted, and deleted by Docker, and their data persists even after the container is stopped or deleted. They are ideal for persistent data storage, databases, or shared data between containers.

• Bind Mounts: Link a directory or file on the host machine directly to a directory or file inside the container. Docker does not manage data storage directly; it only creates a mount point. Changes in the container's filesystem at this point are reflected on the host machine and vice versa. They are convenient for:

  • Development: Mounting source code into the container for instant reflection of changes.
  • Configuration: Passing configuration files from the host to the container.
  • Access to host resources: Providing the container access to specific files or directories on the host.

Main differences:

Characteristic	Volume	Bind Mount
Management	Docker fully manages storage	Docker only creates a mount point
Lifecycle	Separate from the container	Tied to the existence of the host directory/file
Performance	Often optimized for I/O	Depends on the host filesystem performance
Portability	More portable via Dockerfile/Compose	Less portable, depends on host structure
Isolation	Provides better isolation from the host	Less isolated from the host filesystem

Example of using a volume in a Dockerfile:

# Using a volume
VOLUME /app/data

Example of using a bind mount when running a container:

# Mounting a directory
docker run -v /path/on/host:/path/in/container my_image

Example of using a volume when running a container:

# Using a named volume
docker run -v myvolume:/path/in/container my_image