How to share data between Docker containers?

Sharing Data between Docker Containers

Sharing data between Docker containers is a common requirement in many applications. Docker provides several ways to achieve this, each with its own advantages and trade-offs. In this answer, we'll explore the different methods for sharing data between Docker containers.

Volumes

Volumes are the recommended way to share data between Docker containers. Volumes are persistent data storage that exists outside of the container's file system and can be shared among multiple containers. Volumes can be created and managed by Docker, or they can be host-mounted, which means they are stored on the host machine's file system.

Here's an example of how to create and use a volume in Docker:

To create a volume, you can use the docker volume create command:

docker volume create my-volume

Then, you can mount the volume to a container using the -v or --mount flag:

docker run -v my-volume:/data my-app

or

docker run --mount source=my-volume,target=/data my-app

Volumes provide several advantages, such as:

• Data persistence: Volumes are independent of the container's lifecycle, so data will persist even if the container is stopped, deleted, or re-created.
• Performance: Volumes can provide better I/O performance than bind mounts (explained later) because they are managed by Docker.
• Ease of use: Volumes are easy to create, manage, and share among containers.

Bind Mounts

Bind mounts are another way to share data between Docker containers. Bind mounts map a directory on the host machine to a directory inside the container. This allows you to share data between the host and the container, or between multiple containers.

Here's an example of how to use a bind mount:

To use a bind mount, you can specify the host directory and the container directory when running the container:

docker run -v /host/path:/container/path my-app

or

docker run --mount type=bind,source=/host/path,target=/container/path my-app

Bind mounts have some advantages, such as:

• Flexibility: You can share any directory on the host machine with the container.
• Direct access: Containers can directly access the host's file system, which can be useful for certain use cases.

However, bind mounts also have some drawbacks:

• Portability: Bind mounts are host-dependent, which means the container may not work the same way on different host machines.
• Performance: Bind mounts can have lower performance than volumes, especially for high-I/O workloads.

tmpfs Mounts

tmpfs mounts are in-memory file systems that can be used to share data between containers. These are useful for storing temporary data that doesn't need to persist beyond the container's lifetime, such as caching or session data.

Here's an example of how to use a tmpfs mount:

To use a tmpfs mount, you can specify the mount type and the container directory when running the container:

docker run --mount type=tmpfs,destination=/temp my-app

tmpfs mounts have the following advantages:

• Ephemeral data: Data stored in a tmpfs mount is volatile and will be lost when the container is stopped or removed.
• Performance: tmpfs mounts are stored in the host's memory, which can provide better performance than disk-based storage for certain workloads.

However, tmpfs mounts also have some limitations:

• Size: The size of the tmpfs mount is limited by the available memory on the host machine.
• Persistence: Data stored in a tmpfs mount is not persistent, so it's not suitable for storing data that needs to be retained beyond the container's lifetime.

In summary, Docker provides several ways to share data between containers, each with its own advantages and trade-offs. Volumes are the recommended approach for most use cases, as they provide data persistence, good performance, and ease of use. Bind mounts offer more flexibility but can be less portable, while tmpfs mounts are useful for temporary, in-memory data storage.