巨大な IT サービスの管理者と同様に Falcot Corp の管理者もまた、新しいマシンへシステムを素早く (可能であれば自動的に) インストール (または再インストール) するツールを必要としています。

自動インストールの要求に応えるためのさまざまな解決策が存在します。一方では、SystemImager などの一般的なツールが存在します。こちらの解決策ではテンプレートマシンに基づくイメージを事前に準備し、そのイメージを目標のシステムで展開します。他方では、標準的な Debian インストーラが存在します。こちらの解決策ではインストール作業中に尋ねられる質問の回答を含めた設定ファイルを事前に準備し、この設定ファイルに基づいて目標のシステムを設定します。両者の折衷案として、FAI (Fully Automatic Installer) などのハイブリッドツールが存在します。こちらの解決策ではパッケージングシステムでシステムをインストールし、自分自身の機能を使って大規模な配備に特有のタスク (起動、パーティショニング、設定など) をこなします。

Each of these solutions has its pros and cons: SystemImager works independently from any particular packaging system, which allows it to manage large sets of machines using several distinct Linux distributions. It also includes an update system that doesn't require a reinstallation, but this update system can only be reliable if the machines are not modified independently; in other words, the user must not update any software on their own, or install any other software. Similarly, security updates must not be automated, because they have to go through the centralized reference image maintained by SystemImager. This solution also requires the target machines to be homogeneous, otherwise many different images would have to be kept and managed (an amd64 image won't fit on a powerpc machine, and so on).

On the other hand, an automated installation using debian-installer can adapt to the specifics of each machine: the installer will fetch the appropriate kernel and software packages from the relevant repositories, detect available hardware, partition the whole hard disk to take advantage of all the available space, install the corresponding Debian system, and set up an appropriate bootloader. However, the standard installer will only install standard Debian versions, with the base system and a set of pre-selected “tasks”; this precludes installing a particular system with non-packaged applications. Fulfilling this particular need requires customizing the installer… Fortunately, the installer is very modular, and there are tools to automate most of the work required for this customization, most importantly simple-cdd (CDD being an acronym for Custom Debian Derivative). Even this solution, however, only handles initial installations; this is usually not a problem since the APT tools allow efficient deployment of updates later on.

We will only give a rough overview of FAI, and skip SystemImager altogether (which is no longer in Debian, but available as a third-party package), in order to focus more intently on debian-installer and simple-cdd, which are more interesting in a Debian-only context.

d-i netcfg/hostname string worker
d-i netcfg/hostname seen false

menuentry --hotkey=i 'Install' {
    set background_color=black
    linux    /install.amd/vmlinuz preseed/file=/cdrom/preseed.cfg locale=en_US.UTF-8 keymap=us language=us country=US vga=788 --- quiet 
    initrd   /install.amd/initrd.gz
}

label install
        menu label ^Install
        kernel [...]
        append preseed/file=/cdrom/preseed.cfg locale=en_US.UTF-8 keymap=us language=us country=US vga=788 initrd=/install.amd/initrd.gz --- quiet

default vmlinuz
append preseed/file=/hd-media/preseed.cfg locale=en_US.UTF-8 keymap=us language=us country=US vga=788 initrd=initrd.gz  --