Category Archives: docker

Using Duplicity to back up to Linode Object Storage

I migrated my home server from Gentoo Linux to Flatcar Container Linux a little while back, but hadn’t yet migrated the document backups the old server was making. I was using Duplicity to back up documents to the free space within a Linode VPS, but an increase in the size of the backup set was causing the VPS to run out of disk space. With the new server, I decided to try moving the backups from the VPS to Object Storage. (This is an S3-compatible system, so you can probably adapt these instructions to other S3-compatible storage systems…or to Amazon S3 itself. In figuring this out, I started with example configurations for other S3-compatible services and tweaked where necessary.)

I’m using the wernight/duplicity container to back up files. It needs to be provided two persistent volumes, one for your GnuPG keyring and another for cache. The data to be backed up should also be provided to it as a volume. Access credentials for Linode Object Storage should be stored in an environment file.

To make working with containerized Duplicity more like Duplicity on a non-containerized system, you might wrap it in a shell script like this:

#!/usr/bin/env bash
docker run -it --rm --user 1000 --env-file /mnt/ssd/container-state/duplicity/env -v /mnt/ssd/container-state/duplicity/gnupg:/home/duplicity/.gnupg -v /mnt/ssd/container-state/duplicity/cache:/home/duplicity/.cache/duplicity -v /mnt/storage/files:/mnt/storage/files wernight/duplicity $*

(BTW, if you’re not running a container system, you can invoke an installed copy of Duplicity with the same options taken by this script.)

My server hosts only my files, so running Duplicity with my uid is sufficient. On a multi-user system, you might want to use root (uid 0) instead. Your GnuPG keyring gets mapped to /home/duplicity/.gnupg and persistent cache gets mapped to /home/duplicity/.cache/duplicity. /mnt/storage/files is where the files I want to back up are located.

The zeroth thing you should do, if you don’t already have one, is create a GnuPG key. You can do that here with the script above, which I named duplicity on my server:

./duplicity gpg --generate-key
./duplicity gpg --export-secret-keys -a

FIrst thing you need to do (if you didn’t just create your key above) is to store your GnuPG (or PGP) key with Duplicity. Your backups will be encrypted with it:

./duplicity gpg --import /mnt/storage/files/documents/my_key.asc

Once it’s imported, you should probably set the trust on it to “ultimate,” since it’s your key:

./duplicity gpg --update-trustdb

One last thing we need is your key’s ID…or, more specifically, the last 8 digits of it, as this is how you tell Duplicity what key to use. Take a look at the output of this command:

./duplicity gpg --list-secret-keys

One of these (possibly the only one in there) will be the key you created or imported. It has a 32-digit hexadecimal ID. We need just the last 8 digits. For mine, it’s 92C7689C.

Next, pull up the Linode Manager in your browser and select Object Storage from the menu on the left. Click “Create Bucket” and follow the prompts; make note of the name and the URL associated with the bucket, as we’ll need those later. Switch to the access keys tab and click “Create Access Key.” Give it a label, click “Submit,” and make note of both the access key and secret key that are provided.

Your GPG key’s passphrase and Object Storage access key should be stored in an environment file. Mine’s named /mnt/ssd/container-state/duplicity/env and contains the following:


Now we can run a full backup. Running Duplicity on Linode Object Storage (and maybe other S3-compatible storage) requires the –allow-source-mismatch and –s3-use-new-style options:

./duplicity duplicity --allow-source-mismatch --s3-use-new-style --asynchronous-upload --encrypt-key 92C7689C full /mnt/storage/files/documents s3://

“full” specifies a full backup; replace with “incr” for an incremental backup. Linode normally provides the URL with the bucket name as a subdomain of the server instead of as part of the path; you need to rewrite it from https://bucket-name.server-addr to s3://server-addr/bucket-name.

After sending a full backup, you probably want to delete the previous full backups:

./duplicity duplicity --allow-source-mismatch --s3-use-new-style --asynchronous-upload --encrypt-key 92C7689C --force remove-all-but-n-full 1 s3://

You can make sure your backups are good:

./duplicity duplicity --allow-source-mismatch --s3-use-new-style --asynchronous-upload --encrypt-key 92C7689C verify s3:// /mnt/storage/files/documents

Change “verify” to “restore” and you can get your files back if you’ve lost them. Note that restore won’t overwrite a file that exists, so a full restore should be into an empty directory.

Setting up cronjobs (or an equivalent) to do these operations on a regular basis is left as an exercise for the reader. :)

Installing Flatcar Container Linux on Linode

I didn’t see much out there that describes how to set up a Flatcar Container Linux VM at Linode. What follows is what I came up with; it’ll put up a basic system that’s accessible via SSH.

You’ll need a Linux system to prep the installation, as well as about 12 GB of free space. The QEMU-compatible image that is available for download is in qcow2 format; Linode needs a raw-format image. You can download and convert the most recent image as follows (you’ll need QEMU installed, however your distro provides for that):

wget && bunzip2 flatcar_production_qemu_image.img.bz2 && qemu-img convert -f qcow2 -O raw flatcar_production_qemu_image.img tmp.img && mv tmp.img flatcar_production_qemu_image.img && bzip2 -9 flatcar_production_qemu_image.img

You also need a couple of installation tools for Flatcar Container Linux: the installation script and the configuration transpiler. The most recent script is available on GitHub:

wget -O && chmod +x

So’s the transpiler…you can grab the binary from the releases page. You’ll want to grab the latest ct-v*-x86_64-unknown-linux-gnu and rename it to ct.

Next, we need a configuration script. Here’s a basic YAML file that enables SSH login. You’ll want to substitute your own username and SSH public key for mine. Setting the hostname and timezone to appropriate values for you might also be a good idea. Save this as config.yaml:

    - name: salfter
        - sudo
        - wheel
        - docker # or else Docker won't work
        - ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBJQgbySEtaT8SqZ37tT7S4Z/gZeGH+V5vGZ9i9ELpmU salfter@janeway

  # go to to get a new ID
    - device: /dev/sda
    - device: /dev/sdb
    - name: "storage"
        device: "/dev/sdb"
        format: "ext4"
        label: "storage"
        # wipe_filesystem: true
    - filesystem: "storage"
      path: "/docker"
      mode: 0755
    - filesystem: "storage"
      path: "/containerd"
      mode: 0755
    - filesystem: "storage"
      path: "/container-state"
      mode: 0755

    # set hostname
    - path: /etc/hostname
      filesystem: root
      mode: 0644
        inline: |
    # /etc/resolv.conf needs to be a file, not a symlink
    - path: /etc/resolv.conf
      filesystem: root
      mode: 0644
        inline: |

    # set timezone
    - path: /etc/localtime
      filesystem: root
      overwrite: true
      target: /usr/share/zoneinfo/US/Pacific

    # mount the spinning rust
    - name: mnt-storage.mount
      enabled: true
      contents: |
    # store containers on spinning rust
    - name: var-lib-docker.mount
      enabled: true
      contents: |
    - name: var-lib-containerd.mount
      enabled: true
      contents: |
    # Ensure docker starts automatically instead of being socket-activated
    - name: docker.socket
      enabled: false
    - name: docker.service
      enabled: true


Use ct to compile config.yaml to config.json, which is what the Flatcar installer will use:

./ct --in-file config.yaml >config.json

Now it’s time to set up a new Linode. Get whatever size you want. Set it up with any available distro; we’re not going to use it. (I initially intended to leave a small Alpine Linux configuration up to bootstrap and update the system, but you really don’t need it. Uploading and installation can be done with the Finnix rescue system Linode provides.) Shut down the new host, delete both the root and swap filesystems disks that Linode creates, and create two new ones: a 10-GB Flatcar boot disk and a data disk that uses the rest of your available space. Configure the boot disk as /dev/sda and the data disk as /dev/sdb.

Reboot the node in rescue mode. This will (as of this writing, at least) bring it up in Finnix from a CD image. Launch the Lish console and enable SSH login:

passwd root && systemctl start sshd && ifconfig

Mount the storage partition so we can upload to it:

mkdir /mnt/storage && mount /dev/sdb /mnt/storage && mkdir /mnt/storage/install

Make note of the node’s IP address; you’ll need it. I’ll use as an example below.

Back on your computer, upload the needed files to the node…it’ll take a few minutes:

scp config.json flatcar_production_qemu_image.img.bz2 root@

Back at the node, begin the installation…it’ll take a few more minutes:

./ -f flatcar_production_qemu_image.img.bz2 -d /dev/sda -i config.json

Once the installation is complete, shut down the node. In the Linode Manager page for your node, go to the Configurations tab and edit the configuration. For “Select a Kernel” under “Boot Settings,” change from the default “GRUB 2” to “Direct Disk.” /dev/sda is a hard-drive image, not a filesystem image; this will tell Linode to run the MBR on /dev/sda, which will start the provided GRUB and load the kernel.

Now, you can bring up your new Flatcar node. If you still have the console window up, you should see that it doesn’t take long at all to boot…maybe 15 seconds or so once it gets going. Once it’s up, you can SSH in with the key you configured.

From here, you can reconfigure more or less like any other Flatcar installation. If you need to redo the configuration, probably the easiest way to do that is to upload your config.json to /usr/share/oem/config.ign, touch /boot/flatcar/first_boot, and reboot. This will reread the configuration, which is useful for adding new containers, creating a persistent SSH configuration, etc.