Detailed explanation of Bind mounts for Docker data storage

Before reading this article, I hope you have a preliminary understanding of Volumes. For details, please refer to this article:

Docker Data Storage Volumes Detailed Explanation

By default, the reading and writing of container data occurs at the container's storage layer. When the container is deleted, the data on it will be lost. Therefore, we should try to ensure that no write operations occur in the container storage layer. In order to achieve persistent storage of data, we need to choose a solution to save data. Currently, there are several ways:

• Volumes
• Bind mounts
• tmpfs mounts

The following diagram illustrates these three techniques:

Bind mounts

The Bind mounts mode is very similar to Volumes. The difference is that the Bind mounts mode mounts any file or folder on the host to the container, while Volumes essentially mounts an area managed by the Docker service (the default is a folder under /var/lib/docker/volumes) to the container.

The use of bind mounts is similar to that of volumes, and the host files are mounted in the container through -v or --mount parameter. Here is an example:

When using the --mount parameter, you need to specify type=bind :

$ docker run -d \
 --name=nginxtest \
 --mount type=bind,source=/usr/local/web,destination=/usr/share/nginx/html \
 nginx:latest

The above example mounts the /usr/local/web folder on the host to the /usr/share/nginx/html folder in the container.

Or use the -v parameter:

$ docker run -d \
 --name=nginxtest \
 -v /usr/local/web:/usr/share/nginx/html \
 nginx:latest

After the mount is successful, the container reads or writes data from the /usr/share/nginx/html directory, which actually reads or writes data from the /usr/local/web directory of the host. Therefore, Volumes or Bind mounts can also be seen as a way for containers and hosts to share files.

If you use Bind mounts to mount a host directory to a non-empty directory in a container, the files in the non-empty directory in the container will be hidden, and the files that the container can access when accessing this directory are all from the host directory. This is also the biggest behavioral difference between Bind mounts mode and Volumes mode.

Bind mounts usage scenarios

Please refer to this article: Docker Data Storage Summary

References

https://docs.docker.com/storage/bind-mounts/

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