Packer plugin for ARM images

This plugin lets you take an existing ARM image and modify it on your x86 machine. It is optimized for raspberry pi use case - MBR partition table, with the file system partition being the last partition.

With this plugin, you can:

• Provision new ARM images from existing ones
• Use ARM binaries for provisioning (apt-get install for example)
• Resize the last partition (the filesystem partition in the raspberry pi) in case you need more space than the default.

Tested for Raspbian images built on Ubuntu 19.10. It is based partly on the chroot AWS provisioner, though the code was copied to prevent AWS dependencies.

How it works

The plugin runs the provisioners in a chroot environment. Binary execution is done using qemu-arm-static, via binfmt_misc.

Dependencies

This builder uses the following shell commands:

• qemu-user-static - Executing arm binaries. This is optional as the released binary can use embedded versions of qemu-aarch64-static and qemu-arm-static. If you have one installed, it will be used instead of the embedded ones.
• losetup - To mount the image. This command is pre-installed in most distributions.

To install the needed binaries on derivatives of the Debian Linux variant:

sudo apt install qemu-user-static

Fedora:

sudo dnf install qemu-user-static

Archlinux:

pacman -S qemu-arm-static

Other commands that are used are (that should already be installed) : mount, umount, cp, ls, chroot.

To resize the filesystem, the following commands are used:

• e2fsck
• resize2fs

To provide custom arguments to qemu-arm-static using the qemu_args config, gcc is required (to compile a C wrapper).

Note: resizing is only supported for the last active partition in an MBR partition table (as there is no need to move things).

This plugin uses the following kernel feature:

• support for /proc/sys/fs/binfmt_misc so that ARM binaries are automatically executed with qemu

Operation

This provisioner allows you to run packer provisioners on your ARM image locally. It does so by mounting the image on to the local file system, and then using chroot combined with binfmt_misc to the provisioners in a simulated ARM environment.

Configuration

To use, you need to provide an existing image that we will then modify. We re-use packer's support for downloading ISOs (though the image should not be an ISO file). Supporting also zipped images (enabling you downloading official raspbian images directly).

See raspbian_golang.json and config.go for details. For configuration reference, see the builder doc.

Note if your image is arm64, set qemu_binary to qemu-aarch64-static in your configuration json file.

Compiling and Testing

Building

As this tool performs low-level OS manipulations - consider using a VM to run this code for isolation. While this is recommended, it is not mandatory.

This project uses go modules for dependencies introduced in Go 1.11. To build:

git clone https://github.com/solo-io/packer-plugin-arm-image
cd packer-plugin-arm-image
go mod download
go build

Running with Vagrant

This project includes a Vagrant file and helper script that build a VM run time environment. The run time environment has custom provisions to build an image in an iterative fashion (thanks to @tommie-lie for adding this feature).

To use the Vagrant environment, run the following commands:

git clone https://github.com/solo-io/packer-plugin-arm-image
cd packer-plugin-arm-image
vagrant up

To build an image edit samples/raspbian_golang.json (or set PACKERFILE to point to your json config), and use vagrant provision like so:

vagrant provision --provision-with build-image

The example config produces an image with go installed and extends the filesystem by 1GB.

That's it! Flash it and run!

Running locally

This builder requires root permissions as it performs low level machine operations. To run it locally, you can set PACKER_CONFIG_DIR back to your local home before sudo-ing to packer. For example:

PACKER_CONFIG_DIR=$HOME sudo -E $(which packer) build .

Running with Docker

Prerequisites

Docker needs capability of creating new devices on host machine, so it can create /dev/loop* and mount image into it. While it may be possible to accomplish with multiple --device-cgroup-rule and --add-cap, it's much easier to use --privileged flag to accomplish that. Even so, it is considered bad practice to do so, do it with extra precautions. Also because of those requirements rootless will not work for this container.

Option 1: Clone this repo and build the Docker image locally

Build the Docker image locally

docker build -t packer-builder-arm .

Build the samples/raspbian_golang.json Packer image

docker run \
  --rm \
  --privileged \
  -v /dev:/dev \
  -v ${PWD}:/build:ro \
  -v ${PWD}/packer_cache:/build/packer_cache \
  -v ${PWD}/output-arm-image:/build/output-arm-image \
  -e PACKER_CACHE_DIR=/build/packer_cache \
  packer-builder-arm build samples/raspbian_golang.json

Option 2: Run the published Docker image

Alternatively, you can use the ghcr.io/solo-io/packer-plugin-arm-image that's built off latest master without needing to clone this repository.

docker run \
  --rm \
  --privileged \
  -v /dev:/dev \
  -v ${PWD}:/build:ro \
  -v ${PWD}/packer_cache:/build/packer_cache \
  -v ${PWD}/output-arm-image:/build/output-arm-image \
  ghcr.io/solo-io/packer-plugin-arm-image build samples/raspbian_golang.json

That's it, flash it and run!

Running Standalone

packer build samples/raspbian_golang.json

Flashing

We have a post-processor stage for flashing.

Golang flasher

go build cmd/flasher/main.go

It will auto-detect most things and guides you with questions.

dd

(Tested on MacOS)

# find the identifier of the device you want to flash
diskutil list

# un-mount the disk
diskutil unmountDisk /dev/disk2

# flash the image, go for a coffee
sudo dd bs=4m if=output-arm-image/image of=/dev/disk2

# eject the disk
diskutil eject /dev/disk2

Cookbook

Raspberry Pi Provisioners

Enable ssh

{
  "type": "shell",
  "inline": ["touch /boot/ssh"]
}

Set WiFi password

set the user variables name wifi_name and wifi_password, then:

{
  "type": "shell",
  "inline": [
    "echo 'network={' >> /etc/wpa_supplicant/wpa_supplicant.conf",
    "echo '    ssid=\"{{user `wifi_name`}}\"' >> /etc/wpa_supplicant/wpa_supplicant.conf",
    "echo '    psk=\"{{user `wifi_password`}}\"' >> /etc/wpa_supplicant/wpa_supplicant.conf",
    "echo '}' >> /etc/wpa_supplicant/wpa_supplicant.conf"
    ]
}

Add ssh key to authorized keys, enable ssh, disable password login

This example locks down the image to only use your current ssh key. Disabling password login makes it extra secure for networked environments.

Note: this example requires you to run the plugin without a VM, as it copies your local ssh key.

{
  "variables": {
    "ssh_key_src": "{{env `HOME`}}/.ssh/id_rsa.pub",
    "image_home_dir": "/home/pi"
  },
  "builders": [
    {
      "type": "arm-image",
      "iso_url": "https://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-2017-12-01/2017-11-29-raspbian-stretch-lite.zip",
      "iso_checksum": "sha256:e942b70072f2e83c446b9de6f202eb8f9692c06e7d92c343361340cc016e0c9f"
    }
  ],
  "provisioners": [
    {
      "type": "shell",
      "inline": [
        "mkdir {{user `image_home_dir`}}/.ssh"
      ]
    },
    {
      "type": "file",
      "source": "{{user `ssh_key_src`}}",
      "destination": "{{user `image_home_dir`}}/.ssh/authorized_keys"
    },
    {
      "type": "shell",
      "inline": [
        "touch /boot/ssh"
      ]
    },
    {
      "type": "shell",
      "inline": [
        "sed '/PasswordAuthentication/d' -i /etc/ssh/sshd_config",
        "echo >> /etc/ssh/sshd_config",
        "echo 'PasswordAuthentication no' >> /etc/ssh/sshd_config"
      ]
    }
  ]
}

A complete example

See everything included in here: samples/pi-secure-wifi-ssh.json. Build like so:

sudo packer build  -var wifi_name=SSID -var wifi_password=PASSWORD samples/pi-secure-wifi-ssh.json
# or  if running from vagrant ssh:
sudo packer build  -var wifi_name=SSID -var wifi_password=PASSWORD /vagrant/samples/pi-secure-wifi-ssh.json