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Packer and Ansible with VirtualBox
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packer-and-ansible-with-virtualbox.md

Packer and Ansible with VirtualBox

NOTE: This gist is accompanied by my git repository example-of-packer-and-ansible-with-virtualbox. It contains an example of using Packer and Ansible to create a CentOS 7 VirtualBox machine image.

There did not seem to be much information out there on the internet for this so it seemed worthwhile to pass on this knowledge.

Packer from Hashicorp is a tool for creating machine images. It can be used with plugins, called Provisioners, to extend it.

I use the Ansible Provisioner to execute an Ansible playbook to configure the internals of the virtual machine.

Packer also includes plugins for building the image under various Hypervisors. One such is the VirtualBox Builders :

This example creates 2 OVF images :

  • centos-7-from-iso
  • centos-7-base (built upon the centos-7-from-iso image)

centos-7-from-iso image

This image is created from the CentOS 7 CDROM ISO installer.

It uses the Kickstart tool to automate the installation of CentOS.

Our Kickstart file is based on a template centos-7-from-iso/centos-kickstart.cfg.tpl and configures such OS installation details as :

  • chosen language
  • keyboard layout
  • root user settings (no password, no shell)
  • selinux settings (enabled and enforcing)
  • packages to be installed (just "core")
  • install cloud-init package. This provides us with a convenient way to pass configuration data and commands into a VM on first boot. This is used by the packer builder for centos-7-base.
  • configure root SSH authorized_keys to allow Packer to connect via SSH to the VM to run shell commands.
  • reboot at end of installation
#         centos-7-from-iso/centos-kickstart.cfg.tpl
install
cdrom
lang en_GB.UTF-8
keyboard uk
timezone UTC
network --bootproto=dhcp
rootpw --lock
auth --enableshadow --passalgo=sha512 --kickstart
firewall --disabled
selinux --enforcing
bootloader --location=mbr
text
skipx
zerombr
clearpart --all --initlabel
autopart
firstboot --disable
reboot

%packages --instLangs=en_GB.utf8 --nobase --ignoremissing --excludedocs
@core
%end

# ------------------ anaconda post installation script ----------------------------
# Will do the yum update in the centos-7-base build instead
%post --log=/root/ks.log

echo "Start Anaconda Kickstart post-install script"

# Install cloud-init (will be configured at end of packer shell)
yum install -y cloud-init

# Save below ssh key to /root/.ssh to avoid using a password
[ ! -d /root/.ssh ] && mkdir /root/.ssh
chmod 700 /root/.ssh
PACKER_SSH_PUBLIC_KEY='${ssh_public_key}'
echo "PACKER_SSH_PUBLIC_KEY=$${PACKER_SSH_PUBLIC_KEY}"
echo "$${PACKER_SSH_PUBLIC_KEY}" > /root/.ssh/authorized_keys
chmod 600 /root/.ssh/authorized_keys
restorecon -R /root/.ssh

echo "Finished Anaconda Kickstart post-install script"
%end

The kickstart file is templated to enable us to pass the root authorized public SSH key into it from the packer.pkr.hcl as below snippet :

source "file" "kickstart-config" {
  content = templatefile("centos-kickstart.cfg.tpl", {
    ssh_public_key = file("~/.ssh/my-ssh-key-packer-builder.pub")
  })
  target                    =  "${path.root}/kickstart-cdrom/ks.cfg"
}

The kickstart config file is supplied to the VM via a mounted CDROM, configured in the packer.pkr.hcl as below snippet :

  # Create and attach a CD containing the centos kickstart config file (kickstart searches for volumes with label "OEMDRV")
  cd_files                  = [
    "${path.root}/kickstart-cdrom/ks.cfg"
  ]
  cd_label                  = "OEMDRV"
  boot_command              = ["<wait><enter>"]   # Send ENTER key to start installation promptly
  boot_wait                 = "5s"

The above shows the keystrokes "<wait><enter>" that are passed to the VM and the CentOS Anaconda Installater to force the installation to start immediately.

After the CentOS installation has completed, then a Shell script is executed by Packer as in packer.pkr.hcl below :

  provisioner "shell" {
    execute_command = "sudo -S sh '{{ .Path }}'"
    inline          = [
      # Configure cloud-init with NoCloud datasource (otherwise cloud-init service wont start on next bootup)
      "echo 'datasource_list: [ NoCloud, None ]' > /etc/cloud/cloud.cfg.d/01_ds-identify.cfg",
    ]
    inline_shebang  = "/bin/sh -e -x"
  }

This configuration to cloud-init will ensure that it is invoked on next bootup. This will occur during the centos-7-base packer build.

Note: This shell script is run by Packer via SSH using the root user as defined in packer.pkr.hcl here :

  # Use root and an ssh key (note : the ssh pub key is installed in the Kickstart post-install script)
  ssh_username              = "root"
  ssh_private_key_file      = "~/.ssh/my-ssh-key-packer-builder"
  ssh_clear_authorized_keys = "true"

Note that the ssh_clear_authorized_keys=true will ensure that the Packer key is removed and wont be in the output image. Otherwise this would be a security risk.

The VirtualBox image is then exported as an OVF-format file to the centos-7-from-iso/output directory.

centos-7-base image

This image is built upon the centos-7-from-iso OVF image.

It obtains this image from centos-7-from-iso/output directory.

The centos-7-base image is intended to be a base image for all our other image builds and so we want to include into it some fundamentals such as :

  • an administrative user centos (seperate and distinct from root user). This is similar to AWS CentOS AMI images.
  • run the yum update to fully update the system
  • install yum-cron package to update the system nightly

Many other configurations may be desired in your base image. I use Ansible to accomplish these since it is more suited to the job than mere shell scripts.

The centos-7-from-iso OVF filename and path is configured in the packer.pkr.hcl using the source_path attribute :

variable "centos_vbox_iso_to_ovf_filenamepath" {
  type    = string
  default = "${env("CENTOS_VBOX_ISO_TO_OVF_FILENAMEPATH")}"
}
....
source "virtualbox-ovf" "build" {
  vm_name                   = "my-centos-7-base"
  guest_additions_mode      = "attach"
  headless                  = "false"
  source_path               = "${var.centos_vbox_iso_to_ovf_filenamepath}"

The filenamepath is found by the ./packer-build-image.sh and exported as an environment variable CENTOS_VBOX_ISO_TO_OVF_FILENAMEPATH into Packer.

Packer will start the VM using this OVF file. It will pass information into it to cloud-init via an attached floppy disk as defined in packer.pkr.hcl here :

  floppy_files              = [
    "${path.root}/cloud-init-floppy/meta-data",
    "${path.root}/cloud-init-floppy/user-data"
  ]
  floppy_label              = "cidata"

The cloud-init files are created via the packer HC, as below :

locals {
  instance_id = uuidv4()      # Use random instance_id. Otherwise if it does not change then cloud-init "first boot" event will not occur.
}
source "file" "cloud-init-user-data" {
  content                   =  templatefile("cloud-init-user-data.tpl", {
    "centos_user_ssh_public_key" = file("~/.ssh/my-ssh-key-packer-builder.pub")
  })
  target                    =  "${path.root}/cloud-init-floppy/user-data"
}
source "file" "cloud-init-meta-data" {
  content                   =  "instance-id: ${local.instance_id}"
  target                    =  "${path.root}/cloud-init-floppy/meta-data"
}

cloud-init will read and action these files. The user-data file ensures that a centos user will be created as below :

#cloud-config
users:
  - name: centos
    gecos: administrative user
    lock_passwd: true
    ssh_authorized_keys:
      - ${centos_user_ssh_public_key}
    sudo: "ALL=(ALL) NOPASSWD: ALL"

# Avoid it messing with network
network:
  config: disabled

# Avoid it trashing the host keys
ssh_deletekeys: false

The centos user is then used by Packer to connect to the VM via SSH using our SSH Key ~/.ssh/my-ssh-key-packer-builder. Packer can then run the Ansible playbook and shell scripts via this SSH connection.

  provisioner "ansible" {
    # galaxy_file     = "./ansible/requirements.yml"
    playbook_file   = "./ansible/playbook.yml"
    # roles_path      = "./ansible/roles"
    user            = "centos"
    use_proxy       = false
    extra_arguments = [
      "-e YUM_UPDATE_ENABLED='${var.yum_update_enabled}'",
      "-v"
    ]
  }

Above we can see that the Ansible Provisioner is configured to use the new centos user. It is passing the yum_update_enabled variable. Currently no roles are used in the playbook so those lines are commented out.

Finally shell scripts are invoked by Packer over the SSH connection to :

  • reboot the VM to ensure the yum updates have been fully applied
  • wait for reboot
  • clean sensitive information (ssh keys and bash history) as below :
  provisioner "shell" {
    execute_command = "sudo -S sh '{{ .Path }}'"
    inline          = [
      "echo '# Shredding sensitive data for user root...'",
      "[ -f /root/.ssh/authorized_keys ] && shred -u /root/.ssh/authorized_keys",
      "[ -f /root/.bash_history ] && shred -u /root/.bash_history",
      "echo '# Shredding sensitive data for user centos...'",
      "[ -d /home/centos ] && [ -f /home/centos/.bash_history ] && shred -u /home/centos/.bash_history",
      "sync; sleep 1; sync"
    ]
    inline_shebang  = "/bin/sh -e -x"
  }

The VirtualBox image is then exported as an OVF-format file to the centos-7-base/output directory.

Scripts

The following scripts help to create, develop and debug the packer images :

  • packer-build-image.sh
    • this will start the packer build
    • it also installs any required ansible roles from Ansible Galaxy
    • and also validates the ansible playbook and packer hcl file
  • ansible-debug-run.sh
    • this can be used to re-run a failed ansible playbook during the packer build
    • this is possible because Packer is configured to wait on error via the -on-error=ask argument: 
      packer build ${ARG_DEBUG} -on-error=ask packer.pkr.hcl 2>&1 | tee packer.log
    • this enables fixing and re-running of the ansible and is faster than just re-running packer-build-image.sh
  • ssh-connect-to-packer-builder.sh
    • provide convenient SSH connection to a running packer build VM, for debugging purposes.

Summary

VirtualBox can be used with Packer and Ansible to create machine images from ISO Installer files and from other VirtualBox OVF image files.

The speed of running the Ansible playbook and the import/export of OVF files was found to be slower than expected. If it was faster than AWS AMI it could have provided an "on-premise" quick packer/ansible development environment before a final creation of AMI on AWS. Maybe this could be improved using different network setup on the VirtualBox (host/nat/bridged).

Regardless there are use-cases for rolling your own VirtualBox images and using Packer and Ansible will help to automate the creation of these.

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