How to mount directory without restarting docker

With the popularity of Docker, a large number of applications have begun to be deployed in Docker containers. Docker's portability and isolation advantages greatly improve application deployment efficiency and stability. However, due to the isolation nature of Docker containers, sometimes people feel a little helpless. This article will introduce a method to mount a directory without restarting the Docker container.

First, we need to understand Docker’s data volume. A data volume is a mechanism used to save data in a Docker container. It can mount a local directory into a Docker container so that the data in the container can be persisted to the local disk. When starting a Docker container, you can specify a local directory to mount, as shown below:

docker run -v /localdir:/containerdir image_name

Among them, /localdir is the local directory, and /containerdir is is the directory within the container, image_name is the name of the Docker image.

However, when we need to modify the mounting relationship of the directory, we generally need to restart the Docker container. This will lead to increased application downtime and affect the user experience. So, how to modify the mounting directory without restarting the Docker container?

A simple way is to use the mount command. The mount command can realize the mounting and unmounting operations of the file system. Using it, we can change the mounting directory without restarting the Docker container. The specific steps are as follows:

1. Check the mounting status of the current container:

docker inspect -f '{{json .Mounts}}' container_name

Among them, container_name refers to the name of the Docker container.

After executing the above command, the mounting directory information in the container will be returned. The format is as follows:

[
   {
      "Type": "bind",
      "Source": "/var/data",
      "Destination": "/app/data",
      "Mode": "",
      "RW": true,
      "Propagation": "rprivate"
   }
]

Among them, Type is the mounting type, Source is the local directory, Destination is the directory in the container, RW indicates read and write permissions.

2. Uninstall the current mounting directory:

mount --make-rprivate /var/data
umount /var/data

In the above command, the --make-rprivate option is used to set the directory as private permissions to avoid affecting other processes. The umount command is used to uninstall the directory.

3. Mount the new directory:

mount --bind /new/data /var/data

In the above command, we mount the new directory to the original directory to change the directory.

Through the above steps, we have successfully changed the mounting directory without restarting the Docker container. It should be noted that if there are files in the directory that are being used, you need to stop all processes occupying the directory before modification to avoid data loss.

Docker provides an efficient and convenient containerized deployment solution, but in actual application, we need to fully understand its isolation characteristics and learn to use relevant techniques to better deal with various problems. Through the introduction of this article, I believe you have mastered a method to mount a directory without restarting the Docker container. I hope it can help you better cope with actual application scenarios.

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