Instructions based on Debian 6.0 "squeeze":

sudo apt-get install debootstrap qemu-kvm virtinst libvirt-bin
(On Debian 5.0 "lenny":
 use kvm instead of qemu-kvm,
 install debootstrap from the latest Debian stable release)
sudo adduser $USER libvirt
dd if=/dev/zero of=hackage-docs.disk bs=1024 count=5242880
/sbin/mke2fs -F hackage-docs.disk
UUID=`/sbin/blkid -s UUID -o value hackage-docs.disk`
mkdir mnt
sudo mount hackage-docs.disk mnt -o loop
sudo debootstrap stable mnt
sudo UUID="$UUID" chroot mnt /bin/bash
    apt-get update
    apt-get install linux-image-amd64 extlinux openssh-server
    extlinux-update
    sed -i -e "s#^EXTLINUX_PARAMETERS.*#EXTLINUX_PARAMETERS=\"ro quiet root=UUID=$UUID console=ttyS0\"#" etc/default/extlinux
    extlinux-update
    sed -i -e "s/#\(.*ttyS0.*\)/\1/" etc/inittab
    echo hackagedocs > /etc/hostname
    passwd
    echo "proc       /proc proc defaults                   0 0" >  /etc/fstab
    echo "UUID=$UUID /     ext2 defaults,errors=remount-ro 0 1" >> /etc/fstab
    echo "auto lo"                >> /etc/network/interfaces
    echo "iface lo inet loopback" >> /etc/network/interfaces
    echo "auto eth0"              >> /etc/network/interfaces
    echo "iface eth0 inet dhcp"   >> /etc/network/interfaces
(On Debian 5.0 "lenny":
    echo "iface eth0 inet static"        >> /etc/network/interfaces
    echo "    address   192.168.142.2"   >> /etc/network/interfaces
    echo "    netmask   255.255.255.0"   >> /etc/network/interfaces
    echo "    network   192.168.142.0"   >> /etc/network/interfaces
    echo "    broadcast 192.168.142.255" >> /etc/network/interfaces
    echo "    gateway   192.168.142.1"   >> /etc/network/interfaces
)
    touch /etc/udev/rules.d/75-persistent-net-generator.rules
    mount /proc
    extlinux --install boot/extlinux
    umount /proc
sudo umount mnt
cat <<EOF > hackage_docs_network.xml
<network>
    <name>hackage_docs_network</name>
    <bridge name="virbr1" />
    <forward mode="nat" />
    <ip address="192.168.142.1" netmask="255.255.255.0">
        <dhcp>
            <range start="192.168.142.2" end="192.168.142.2" />
        </dhcp>
    </ip>
</network>
EOF
sudo virsh net-create hackage_docs_network.xml
virt-install --connect qemu:///system -n hackage-docs-vm -r 1024 --vcpus=1 --nographics -w network=hackage_docs_network --os-type linux --os-variant debiansqueeze --disk path=hackage-docs.disk --hvm --import
(On Debian 5.0 "lenny":
cat <<EOF > hackage_docs_image.xml
<image>
    <name>hackage-docs-vm</name>
    <domain>
        <boot type="hvm">
            <guest>
                <arch>x86_64</arch>
            </guest>
            <os>
                <loader dev="hd" />
            </os>
            <drive disk="hackage-docs.disk" target="hda" />
        </boot>
        <devices>
            <vcpu>1</vcpu>
            <memory>1048576</memory>
            <interface />
        </devices>
    </domain>
    <storage>
        <disk file="hackage-docs.disk" />
    </storage>
</image>
EOF
virt-image   --connect qemu:///system -n hackage-docs-vm -r 1024 --vcpus=1 --nographics -w network=hackage_docs_network hackage_docs_image.xml
)
ssh root@192.168.142.2
    apt-get install build-essential libgmp3-dev libz-dev darcs alex happy hscolour vim
    apt-get clean
    adduser hackage-docs --gecos "" --disabled-password
    su - hackage-docs
        mkdir .ssh
        vi .ssh/authorized_keys
ssh hackage-docs@192.168.142.2
    mkdir downloads
    cd downloads
    wget http://www.haskell.org/ghc/dist/7.4.2/ghc-7.4.2-x86_64-unknown-linux.tar.bz2
    tar -jxf ghc-7.4.2-x86_64-unknown-linux.tar.bz2
    cd ghc-7.4.2
    ./configure --prefix=$HOME/local/ghc-7.4.2
    make install
    echo "export PATH=\"$HOME/local/ghc-7.4.2/bin:\$PATH\"" >> ~/.bashrc
    cd ..
    rm ghc-7.4.2-x86_64-unknown-linux.tar.bz2
    rm -r ghc-7.4.2
ssh hackage-docs@192.168.142.2
    cd downloads
    # For now we need to use a snapshot. Once 1.16 is releases we should
    # be able to just use that, and no need to build Cabal.
    wget http://lambda.haskell.org/~igloo/cabal-1.16-snapshot.tar.bz2
    tar -jxf cabal-1.16-snapshot.tar.bz2
    cd cabal-1.16-snapshot/Cabal
    ghc --make Setup
    ./Setup configure --user
    ./Setup build
    ./Setup install
    cd ../cabal-install
    sh bootstrap.sh
    echo "export PATH=\"$HOME/.cabal/bin:\$PATH\"" >> ~/.bashrc
    cd ../..
    rm cabal-1.16-snapshot.tar.bz2
    rm -rf cabal-1.16-snapshot
ssh hackage-docs@192.168.142.2
    cabal update
    cd downloads
    darcs get http://code.haskell.org/hackage-server
    cd hackage-server
    cabal install -f-build-hackage-server -f-build-hackage-mirror
    cd
    mkdir hackage-docs
    cd hackage-docs
    hackage-build init http://192.168.142.1:8080/
    sed -e "s#@PIDFILE@#$HOME/hackage-docs/hd.pid#" -e "s#@HACKAGEBUILD@#$HOME/.cabal/bin/hackage-build#" -e "s#@DIRECTORY@#$HOME/hackage-docs#" -e "s#@EXTRA@#export PATH=$HOME/local/ghc-7.4.2/bin:$HOME/.cabal/bin:\$PATH#" < ../downloads/hackage-server/docs/run-doc-builder.sh.example > run-doc-builder.sh
    chmod +x run-doc-builder.sh
    echo '*/5 * * * * '"$HOME/hackage-docs/run-doc-builder.sh" | crontab -