How to Backup Docker Volumes

Containers are volumes by default; volumes are an integral feature of Docker containers, which facilitates state2state persistence of data in containers if they have been powered-off and brought up again. However, Docker volumes need the same backups as any other data type — to protect data from accidental deletions or system failures and other unexpected issues. By going through this article, you will be in a position to backup the volumes of Docker and be sure that your data is well secure.

1. Understanding Docker Volumes

Prior to getting started with backing up, it is crucial to grasp the concept of Docker volumes and their functionality. Docker manages volumes as storage units that exist separately from the container's lifecycle. Docker volumes differ from bind mounts as they are stored in a location controlled by Docker and are meant to be easily moved between containers, unlike bind mounts which connect directories on the host machine to directories in the container.

Docker volumes are very handy for saving data that must remain across container restarts or for exchanging data between various containers. It is crucial to regularly back up these volumes to maintain data integrity and availability due to their significance.

2. Preparing for Backup

Accessing the Docker CLI on the host machine where the volume is located is necessary in order to create a backup of a Docker volume. Furthermore, it is crucial to ensure that the container undergoing the backup process is paused to prevent data inconsistencies.

You can stop the container by executing the command provided below:

docker stop

3. Creating a Backup of Docker Volumes

There are several methods to backup Docker volumes, depending on your specific needs and environment. Below are some common approaches.

Method 1: Using docker run and tar

Using a temporary container to build a tarball (compressed archive) of the volume's contents is one of the easiest ways to backup a Docker volume. In this procedure, the volume is mounted to the temporary container, and a backup is made using the tar command. 

Here’s a step-by-step guide:

Run a temporary container:
Use the following command to create a temporary container and mount the volume you want to back up:
docker run --rm -v :/volume -v $(pwd):/backup ubuntu tar -cvf /backup/.tar /volume

1. Replace:

• with the name of your Docker volume.

• with a name for your backup file.

2. This command creates a tarball of the volume's contents and stores it in the current directory on the host machine.

Verify the backup:
After the command completes, verify that the backup file has been created by listing the files in the current directory:
ls -lh .tar

3. This step ensures that the backup process was successful and the file is intact.

Method 2: Using docker cp

The docker cp command, which lets you move files and directories between the host and container filesystems, is another way to backup Docker volumes. This technique comes in very handy for smaller volumes or for backing up individual files or directories inside a disk. 

Start a container with the volume mounted:
If the container is stopped, you can start it with the volume mounted:
docker start

Copy the contents of the volume:
Use the docker cp command to copy the contents of the volume to a directory on the host:
docker cp :/path/in/container /path/on/host

2. Replace:

• with the name or ID of the container.

• /path/in/container with the path where the volume is mounted in the container.

• /path/on/host with the destination path on the host where the backup will be stored.

3. Verify the backup:
   As with the tarball method, it’s important to verify that the files have been copied correctly by listing the contents of the destination directory.

Method 3: Using Docker Volume Plugins

For those using Docker in production environments, there are various Docker volume plugins available that offer advanced features like automatic backups, snapshots, and cloud storage integration. These plugins often provide a more streamlined and scalable solution for managing Docker volume backups.

To use a volume plugin, you typically need to install the plugin on your Docker host and configure it according to your backup requirements. While each plugin has its own setup process, the general steps involve:

Install the plugin:
Install the desired Docker volume plugin using the Docker CLI. For example:
docker plugin install

Create a volume with the plugin:
When creating a Docker volume, specify the plugin to use for the volume:
docker volume create --driver

2.  

3. Configure the backup settings:
   Depending on the plugin, you may be able to configure automatic backups, set retention policies, and specify storage locations.

4. Monitor and verify backups:
   Verify that backup files are created and saved in the right area, and keep an eye on the plugin's logs to make sure backups are operating as planned. 

4. Restoring Docker Volumes from Backup

Restoring a Docker volume from a backup is a straightforward process, essentially the reverse of the backup process.

Method 1: Restoring from a Tarball

If you used the tarball method to back up your volume, you can restore it using the following steps:

Create a new Docker volume:
docker volume create

1. Replace with a name for the new volume.

Restore the tarball to the new volume:
Use the following command to extract the tarball’s contents into the new volume:
docker run --rm -v :/volume -v $(pwd):/backup ubuntu tar -xvf /backup/.tar -C /volume

2. This command unpacks the tarball’s contents into the new volume, effectively restoring the data.

Method 2: Restoring Using docker cp

If you used the docker cp method for backup, you can restore the volume by copying the files back into the container:

Start the container:
docker start

Copy the backup files into the volume:
docker cp /path/on/host :/path/in/container

2. This command copies the files from the host back into the container’s volume.

5. Conclusion

Creating backups of Docker volumes is a necessary step to guarantee data integrity and accessibility in container-based setups. Implementing a strong backup plan, whether through tarball, docker cp, or volume plugins, is crucial to safeguarding data and ensuring fast recovery in case of a failure. Frequently check your backup and restore procedures to confirm they function properly, safeguarding your Docker volumes and applications.