Backup/Restore Docker Data

In this lab, you will learn how to perform Docker backups, including backing up Docker volumes, images, and configurations. You'll also learn how to restore from these backups.

Prerequisites:

• Docker installed on your system
• Basic understanding of Docker containers and volumes
• A sample running container with a volume to back up

Step 1: Setup a Sample Docker Environment

1.1 Create a Sample Docker Container with a Volume

Let's start by creating a container with a volume where containers store persistent data.

• Run a simple container using the nginx web server, creating a volume to store data:

  docker run -d --name my_nginx -v nginx_data:/usr/share/nginx/html -p 8080:80 nginx
  

  • -d: Run the container in detached mode.
  • --name: Assign a name to the container (my_nginx).
  • -v: Create a Docker volume (nginx_data) and mount it to the container.
  • -p: Map port 8080 on your host to port 80 inside the container.

1.2 Verify the Running Container

To verify that your container is running:

docker ps

You should see the my_nginx container running.

1.3 Add Some Data to the Volume

Let’s create a sample file inside the container’s volume:

docker exec my_nginx sh -c "echo 'Hello, Docker Backup!' > /usr/share/nginx/html/index.html"

Now, if you visit http://srvX.lab.npnog.org.np:8080, you should see the message "Hello, Docker Backup!" in your browser.

Step 2: Back Up Docker Volumes

2.1 List Docker Volumes

Check all the Docker volumes on your system:

docker volume ls

You should see nginx_data listed.

2.2 Backup a Docker Volume

Now, let’s back up the nginx_data volume to a tarball:

docker run --rm -v nginx_data:/data -v $(pwd):/backup busybox tar cvf /backup/nginx_data_backup.tar /data

• Explanation:

  • --rm: Automatically remove the container after it’s done.
  • -v nginx_data:/data: Mount the Docker volume (nginx_data) to /data inside the container.
  • -v $(pwd):/backup: Mount the current working directory on the host to /backup inside the container, where the tarball will be stored.
  • busybox: A small utility container for running commands like tar.
  • tar cvf: Create a tarball (compressed file) from the /data directory.

• Result:

  • You should now have a file called nginx_data_backup.tar in your current directory.

Step 3: Back Up Docker Images

3.1 Save the Docker Image

To back up the Docker image used by the container (in this case, nginx), use the docker save command:

docker save -o nginx_image_backup.tar nginx

• This creates a tarball of the nginx image, saving it as nginx_image_backup.tar.

Step 4: Back Up Docker Compose (Optional)

If you're using Docker Compose, backing up the docker-compose.yml file is essential. Simply copy the file to your backup location.

Example:

cp /path/to/docker-compose.yml /path/to/backup/

Step 5: Restore Docker Volumes and Images

5.1 Restore a Docker Volume

To restore a Docker volume from the backup tarball:

1. Remove or stop the current container (optional if necessary):

   docker rm -f my_nginx
   

2. Recreate the volume and restore the data:

   docker volume create nginx_data
   docker run --rm -v nginx_data:/data -v $(pwd):/backup busybox tar xvf /backup/nginx_data_backup.tar -C /data
   

   • This restores the contents of nginx_data_backup.tar into the nginx_data volume.

5.2 Restore a Docker Image

To restore the Docker image from the tarball:

docker load -i nginx_image_backup.tar

• This reloads the nginx image into Docker.

Step 6: Verify the Restore

6.1 Recreate the Container

Now, recreate the my_nginx container using the restored volume and image:

docker run -d --name my_nginx -v nginx_data:/usr/share/nginx/html -p 8080:80 nginx

6.2 Check if Data is Restored

Visit http://srvX.lab.npnog.org.np:8080 again. If the backup and restore were successful, you should see the message "Hello, Docker Backup!" just as before.

Step 7: Automating Backups

7.1 Setting Up a Cron Job for Regular Backups

You can schedule backups to run automatically using cron jobs on Linux systems. To set up a daily backup of the nginx_data volume:

1. Open the crontab editor:

   crontab -e
   

2. Add the following line to schedule the backup at 2 AM every day:

   0 2 * * * docker run --rm -v nginx_data:/data -v /backup:/backup busybox tar cvf /backup/nginx_data_backup.tar /data
   

   This ensures that your volume data is regularly backed up without manual intervention.