Which files are shared between docker container and host?

Which files are shared between Docker container and host?

When working with Docker containers, it is important to understand how files are shared between the container and the host system. Docker provides various mechanisms to facilitate file sharing, allowing data to be accessed and modified by both the container and the host. In this article, we will explore the different ways in which files can be shared between a Docker container and the host system.

1. Volumes

Volumes are the recommended way to share files between a Docker container and the host system. A volume is a directory that exists outside the container's file system and is managed by Docker. It allows data to persist even if the container is stopped or deleted.

To create a volume, you can use the docker volume create command or specify a volume in the docker run command. Once a volume is created, it can be mounted to a specific directory inside the container using the -v or --mount flag.

For example, to create a volume named myvolume and mount it to the /data directory inside the container, you can use the following command:

docker volume create myvolume
docker run -v myvolume:/data mycontainer

Any changes made to the files in the /data directory inside the container will be reflected in the volume on the host system, and vice versa.

2. Bind Mounts

Bind mounts provide another way to share files between the container and the host system. Unlike volumes, bind mounts can be used to share any file or directory on the host system.

To create a bind mount, you need to specify the path to the file or directory on the host system and the path where it should be mounted inside the container using the -v or --mount flag in the docker run command.

For example, to bind mount the /var/www/html directory on the host system to the /var/www/html directory inside the container, you can use the following command:

docker run -v /var/www/html:/var/www/html mycontainer

Any changes made to the files in the /var/www/html directory inside the container will be reflected on the host system, and vice versa.

3. Temporary File Systems

Docker also provides temporary file systems that are not shared between the container and the host system. These file systems are useful in scenarios where you don't want the data to persist after the container is stopped or deleted.

When you run a container, Docker creates a temporary file system for it. Any changes made to the files inside this file system will be lost once the container is stopped or deleted.

4. Image Layers

Image layers are the building blocks of Docker images. Each layer represents an instruction in the Dockerfile. When you run a container, Docker creates a new layer on top of the base image layer.

By default, image layers are read-only and cannot be modified. Any changes made to the files inside a container are stored in a new layer called the container layer. This container layer is separate from the image layers and is not shared with the host system.

Conclusion

In summary, Docker provides several mechanisms to share files between a container and the host system. Volumes are the recommended way to share data, as they allow for persistence even if the container is stopped or deleted. Bind mounts can be used to share any file or directory on the host system. Temporary file systems are useful for scenarios where data persistence is not required. Image layers are read-only and cannot be modified, with any changes made to the container stored in a separate layer.

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