Directory Structure

The directory structure of the project contains quite a few elements. About a third of them are volatile directories which can be removed at any time but for the sake of completenes and for troubleshooting purposes are still listed here.

Directory Structure Overview

<project root>
  ├── artifacts (1)
  │   └── qemu
  │       └── ubuntu_22.raw
  │  
  ├── docker (2)
  │   └── docker-packer
  │  
  ├── documentation (3)
  │   └── ... .adoc
  │  
  ├── http (3)
  │   ├── ubuntu_22.04
  │   │   ├── meta-data
  │   │   └── user-data
  │   └── ...
  │  
  ├── images (4)
  │   ├── ubuntu_22.04.1-server-efi.qcow2
  │   ├── ubuntu_22.04.1-server-efi.vmdk
  │   └── ...
  │  
  ├── install (5)
  │   └── ...
  │  
  ├── iso (6)
  │   ├── ubuntu_22.04
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso.lock
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso.sha256
  │   └── ...
  │  
  ├── lib (7)
  │   ├── packer
  │   │   ├── host.rb
  │   │   ├── iso.rb
  │   │   └── variables.rb
  │   ├── packer.rb
  │   └── password_factory.rb
  │  
  ├── logs (8)
  │   └── ubuntu_22.10.log
  │  
  ├── packer (9)
  │   ├── common.auto.pkrvars.hcl
  │   ├── linux_build.pkr.hcl
  │   ├── linux_sources.pkr.hcl
  │   ├── ubuntu_22.04.1.pkrvars.hcl
  │   ├── variables.pkr.hcl
  │   └── ...
  │  
  ├── provisioners (10)
  │   └── ...
  │  
  ├── Rakefile (11)
  │  
  ├── scripts (12)
  │   ├── convert-diskimage.sh
  │   └── qemu-runner.sh
  │  
  └── templates (13)
      ├── ubuntu_20.04
      │   ├── meta-data.erb
      │   └── user-data.erb
      ├── ubuntu_22.04 -> ubuntu_20.04
      └── ...

artifacts volatile directory where packer is storing its work disks.
docker a git submodule pointing to https://github.com//uroesch/docker-packer.
documentation holds the documentation source file written in Asciidoctor.
http volatile directory used to store the packer configuration files used during installation such as kickstart.cfg or user-data.
images is a volative directory holding all the images resulting from the build process.
install contains the novnc files used to run as a service. Only required when not building with docker.
lib contains a few Ruby libraries required by the Rakefile.
logs volatile directory storing the log from the latest build.
packer contains the whole packer configuration split in various both common and os specific ones.
provisioners a git submodule pointing to the Ansible provisioner.
Rakefile containing the build instructions create an OS image.
scripts contains custom scripts and helpers for post processing and debugging.
templates holds the kickstart.cfg and user-data ERB templates.

Details

`artificats`

Is the directory where packer is storing the working disk of the current bulid. When a packer build process is prematurely is interupted or fails uncontrolled, disk images may remain and block the same OS build from running again. In such an occurrence the whole directory can be removed.

ℹ️	The `docker-packer` wrapper script creates a uniq `artifacts` directory for each build and removes and cleans it up completly when finished.

`docker`

Is only mentioned here because the docker-packer shell script wrapper around the build process is located in there. The docker-packer script creates a temprary artifiacts directory and mounts it inside the docker container. All the other directories such as http, iso, templates among others are also mounted. Additionally the novnc script is being spawned to provide a way to monitor the progress of the build via a websocket on a headless build host.

`documentation`

Contains the projects documentation in the form of asciidoc files. Asciidoc allows for easy inclusion of various graphics libraries and can convert the content into an array of formats such but not limited to HTML and PDF.

`http`

<project root>
  │  
 ...
  │  
  ├── http
  │   ├── rocky_9
  │   │   └── kickstart.cfg
  │   │   
  │   └── ubuntu_22.04
 ...      ├── meta-data
          └── user-data

The http directory is a volatile directory which can be removed befor each build it is recreated before the buld by the Rakefile script.

Under the http directory a sub directory is created for each operating system variant. E.g for a Rocky 9 the directory name is rocky_9 and contains the kickstart.cfg file. For Ubuntu 22.04 the name of the directory is ubuntu_22.04 and contains the subiquity files meta-data and user-data.

`images`

<project root>
  │  
 ...
  │  
  ├── images
  │   ├── rocky_9.1-server-efi.qcow2
  │   ├── rocky_9.1-server-efi.vmdk
  │   ├── ...
  │   ├── ubuntu_22.04.1-server-efi.qcow2
  │   ├── ubuntu_22.04.1-server-efi.vmdk
  │   └── ...
  │  
 ...

In the images directory the images are stored after a successful build.

The file name of each image is using 4 distinct properties delimited by a hyphen -

Release

Distribution name and full release version e.g. rocky for distribution name and 9.1 for major and minor release version. Or ubuntu and 22.04.1 as for an Ubuntu image.

Disk Layout

The second field is the disk layout used for the images. The default is server which uses the default layout of the distribution. There are other options such as pcidss which have to specified at build time. To set the disk layout to something other than server provide the option TARGET=pcidss option when building.

Firmware

Field number 3 is the firmare used during the build. This defaults to efi the only other options is bios. To set the build to BIOS provide the option FIRMWARE=bios when building.

Target Platform

The last indicator is the file extension. There are two tiers of platforms. The .qcow2 extension is used for the stage 1 base build which is then used to build the stage 2 images such as VMware, Hyper-V and Azure. Currently there are 3 stage 2 extensions.

.vmdk for VMware / Vsphere deployments.
.vhdx for Hyper-V hypervisors.
.vhd for deployments in the Azure cloud.

`install`

Contains a few files for running novnc as systemd service on the host. This is the build is not done via the docker-packer script which has this functionality built in.

`iso`

<project root>
  │  
 ...
  │  
  ├── iso
  │   ├── rocky_9
  │   │   ├── Rocky-9.1-x86_64-dvd.iso
  │   │   ├── Rocky-9.1-x86_64-dvd.iso.lock
  │   │   ├── Rocky-9.1-x86_64-dvd.iso.sha256
  │   │   └── ...
  │   │  
  │   ├── ubuntu_22.04
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso.lock
  │   │   ├── ubuntu-22.04.1-live-server-amd64.iso.sha256
  │   │   └── ...
  │   │  
  │   └── ...
  │  
 ...

Per default the iso directory only contains sub directories for each OS via it’s distribution name and the major release number e.g. rocky_9 or ubuntu_22.04.

Initially each sub directory only contains the SHA256 sum file of the ISO image used for the installation. During the first run the ISO file is downloaded and compared with the checksum. Consecutive builds then only do the checksum check against the already downloaded .iso file.

ℹ️	Distributions where the ISO file is not freely available such as Red Hat Enterprise Linux (RHEL) or SUSE Linux Enterprise (SLE) must be downloaded manually and put into the correct sub directory within the tree.

`lib`

Is where the ruby libraries are located used to help with determining a few facts about the environment of the build hosts among other things. Generally this directory should not be touched or changed at all.

`logs`

<project root>
  │  
 ...

  │  
  ├── logs
  │   ├── rocky_9.log
  │   ├── ...
  │   └── ubuntu_22.10.log
  │  
 ...

The build logs all actions in verbose mode into the log directory. Each OS has a dedicated log file base on the distribution name and the major version. E.g rocky_9.log or ubuntu_22.04.log. The log file is overwritten with each consecutive build. In case of an issue the log file has to be analyzed before starting the build again.

Removing the log directory has not consequences. With each build it is recreated.

`packer`

<project root>
  │  
 ...
  │  
  ├── packer
  │   ├── common.auto.pkrvars.hcl
  │   ├── linux_build.pkr.hcl
  │   ├── linux_sources.pkr.hcl
  │   ├── rocky_9.1.pkrvars.hcl
  │   ├── ...
  │   ├── ubuntu_22.04.1.pkrvars.hcl
  │   ├── ...
  │   ├── variables.pkr.hcl
  │   └── ...
  │  
 ...

Within the packer directory are all the instructions for the build contained. There are 3 type of files which govern the build

common.auto.pkrvars.hcl

Is a packer variable file which holds the common parameters used for all OS builds such as disk size and ssh passwords for the provisioner login.

linux_build.pkr.hcl

Holds the instructions how to build each of the target platforms inlcuding the base build. The build file sports 3 components for the workflow these are:

build via the source instructions
provisioner triggering the post installation process via Ansible.
post-processor converting the image from qcow2 into the target format.

linux_sources.pkr.hcl

Defines the two QEMU build stages. Namely stage 1 or base build and the the stage 2 builds for hyper visor or cloud specific builds. More information can be viewed in the packer documentation for QEMU

<distro_N.N>.pkrvars.hcl

Contains the distribution specific variables used for the build such as ISO file name or minor and major version numbers.

variables.pkr.hcl

Each variable in packer has to be defined with a type and possibly a description. The variables.pkr.hcl contains both variable types for the var and local prefix.

`provisioners`

Contains the Ansible roles and playbooks for the post installation steps. This directory is generally a git submodule pointing to an other repository.

`Rakefile`

Is the file used to start an OS build and is invoked with the rake command.

`scripts`

Currently holds two helper scripts one to convert the disk images in the post-processor step called convert-diskimage.sh. Addtionally there is the qemu-runner.sh script which can be used for debugging base images under the images directory or start ISO files found under the iso directory.

`templates`

<project root>
  │  
 ...
  │  
  ├── templates
  │   ├── rocky_9
  │   │   └── kickstart.cfg.erb
  │   ├── ...
  │   │
  │   ├── rhel_9 -> rocky_9
  │   │
  │   ├── ubuntu_20.04
  │   │   ├── meta-data.erb
  │   │   └── user-data.erb
  │   │
  │   ├── ubuntu_22.04 -> ubuntu_20.04
  │   │
  │   └── ...
  │  
 ...

Under the templates directory the OS specific build instructions are stored in the form of ERB templates. Before each build the templates are parsed, populated with the appropriate values and put into the http directory for packer to pass it to the build process.

To minimize duplication only major Red Hat releases get a directory named after the distribution and the major release number. All derivatives such as almalinux, rocky or oraclelinux are symlinked to the original directory.

For Ubuntu releases the instructions can be shared among major release if the same installation technology such as subiquity is used. E.g for Ubuntu 20.04 and Ubuntu 22.04.

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Directory Structure

Directory Structure