Backups are super helpful, especially when you like to blow everything away fairly often. Backing up the data from a Docker container can help you quickly get things up and running again.

Tutorial

My recent post detailed how to setup a UniFi Controller in a Docker container. This tutorial uses that container as an example for creating and restoring backups of data volumes.

Backup

  1. Creating backups is done by producing an archive of the important files on the host filesystem from the container’s data volume.

    $ docker run \
      --rm \ (1)
      --volumes-from unifi-controller \ (2)
      -v $(pwd):/backup \ (3)
      ubuntu tar cvWf /backup/unifi-controller_backup_$(date +%F).tar -C /config unifi-controller (4)
    1 Remove the container when finished.
    2 Attach the data volumes for the container named unifi-controller.
    3 Mount the current directory to /backup in the container.
    4 Using an Ubuntu image, create an archive of the directory /config/unifi-controller in the /backup directory.
  2. Compress the backup.

    $ xz unifi-controller_backup_2020-07-01.tar

Restore

To restore from a backup, just reverse the backup process.

  1. Decompress the backup.

    $ unxz unifi-controller_backup_2020-07-01.tar.xz
  2. Restore the contents of the archive to the data volume.

    $ docker run
      --rm \ (1)
      --volumes-from unifi-controller \ (2)
       -v $(pwd):/backup \ (3)
       ubuntu tar xvf /backup/unifi-controller_backup_2020-07-01.tar -C / (4)
    1 Remove the container when finished.
    2 Attach the data volumes for the container named unifi-controller.
    3 Mount the current directory to /backup in the container.
    4 Using an Ubuntu image, expand the archive in the / directory.

Verify

It’s always important to test your backups. The simplest way to check the backup is with a fresh instance of the container. For the UniFi Controller, this is trivially accomplished.

  1. First, copy the compose file to another directory and give the container a new name.

    $ mkdir unifi-controller2
    $ cp unifi-controller/docker-compose.yml unifi-controller2
    $ cd unifi-controller2
  2. Modify the yaml file to match the following.

    docker-compose.yml
    ---
    version: "2.1"
    services:
      unifi-controller:
        image: linuxserver/unifi-controller
        container_name: unifi-controller2 (1)
        environment:
          - PUID=1000
          - PGID=1000
          - MEM_LIMIT=1024M #optional
        volumes:
          - data:/config
        ports:
          - 3478:3478/udp
          - 10001:10001/udp
          - 8080:8080
          - 8081:8081
          - 8443:8443
          - 8843:8843
          - 8880:8880
          - 6789:6789
        restart: unless-stopped
    
    volumes:
      data:
    1 Name the container unifi-controller2.
  3. Initialize the container.

    $ docker-compose up --no-start
  4. Decompress the backup.

    $ unxz unifi-controller_backup_2020-07-01.tar.xz
  5. Restore the contents of the archive to the new container’s data volume.

    $ docker run
      --rm \
      --volumes-from unifi-controller2 \ (1)
       -v $(pwd):/backup \
       ubuntu tar xvf /backup/unifi-controller_backup_2020-07-01.tar -C /
    1 Attach the data volumes for the new unifi-controller2 container.

    That’s it! The data from your original container should now be duplicated in unifi-controller2.

  6. Now, start unifi-controller2.

    $ docker-compose up -d
  7. Then, open the UniFi Controller’s web UI.

    $ xdg-open http://127.0.0.1:8443
  8. Login just as you would on the unifi-controller container and verify that your restored controller’s configuration matches the original.

You have now learned how to back up and restore the data in a Docker container’s data volume.